Photonic crystal fibers and medical systems including photonic crystal fibers

ABSTRACT

In general, in one aspect, the invention features apparatus that include an assembly including a radiation input port configured to receive radiation from a radiation source and an output port configured to couple the radiation to a photonic crystal fiber, the assembly further including a retardation element positioned to modify a polarization state of the radiation received from the radiation source before it is coupled to the photonic crystal fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

Under 35 USC §119(e)(1), this application claims the benefit ofProvisional Patent Application 60/560,458, entitled “PHOTONIC CRYSTALFIBER APPLICATIONS,” filed on Apr. 8, 2004, Provisional PatentApplication 60/561,020, entitled “PHOTONIC CRYSTAL FIBER APPLICATIONS,”filed on Apr. 9, 2004, Provisional Patent Application 60/584,098,entitled “PHOTONIC CRYSTAL FIBER APPLICATIONS,” filed on Jun. 30, 2004,Provisional Patent Application 60/628,462, entitled “PHOTONIC CRYSTALFIBER APPLICATIONS,” filed on Nov. 16, 2004, Provisional PatentApplication 60/640,536, entitled “OMNIGUIDE PHOTONIC BANDGAP FIBERS FORFLEXIBLE DELIVERY OF CO₂ LASERS IN LARYNGOLOGY,” filed on Dec. 30, 2004,and Provisional Patent Application 60/658,531, entitled “PHOTONICCRYSTAL FIBERS,” filed on Mar. 4, 2005. The contents of all theabove-listed provisional patent applications are hereby incorporated byreference in their entirety.

BACKGROUND

Lasers are prevalent in many areas of medicine today. For example,lasers find application in diverse medical areas, such as surgery,veterinary medicine, dentistry, ophthalmology, and in aesthetic medicalprocedures.

In many of these applications, an optical fiber is used to deliverradiation from a laser to the target region of the patient. Conventionaloptical fibers are excellent waveguides for radiation having wavelengthsin the visible or near-infrared portion of the electromagnetic spectrum(e.g., wavelengths of about 2 microns or less). However, conventionaloptical fibers are, in general, not suitable in applications where highpower laser radiation with relatively long wavelengths is used.Accordingly, many medical laser systems that deliver high power (e.g.,about 10 Watts or more), long wavelength (e.g., greater than about 2microns), do so using an articulated arm that includes opticalcomponents that guide the laser radiation through rigid conduits or freespace from the laser to the target.

SUMMARY

Photonic crystal fibers can be used in medical laser systems to guideradiation from a radiation source (e.g., a laser) to a target locationof a patient. In general, photonic crystal fibers include a regionsurrounding a core that provides extremely effective confinement ofcertain radiation wavelengths to the core. These so-called confinementregions can be formed exclusively from amorphous dielectric materials(e.g., glasses and/or polymers), and can provide effective confinementwhile still being relatively thin. Accordingly, photonic crystal fiberscan include thin, flexible fiber's capable of guiding extremely highpower radiation.

Moreover, photonic crystal fibers can be drawn from a preform, resultingin fibers that are relatively inexpensive to produce compared to otherwaveguides that are not drawn. Fiber manufacturing techniques alsoprovides substantial production capacity, e.g., thousands of meters offiber can be drawn from a single preform. The conversion in the drawprocess from a relatively short preform to very long lengths of fibercan effectively smooth out any perturbations from the desired structurethat exist in the preform, producing low-loss, low-defect fiber.

In general, in a first aspect, the invention features systems, includinga photonic crystal fiber including a core extending along a waveguideaxis and a dielectric confinement region surrounding the core, thedielectric confinement region being configured to guide radiation alongthe waveguide axis from an input end to an output end of the photoniccrystal fiber. The systems also includes a handpiece attached to thephotonic crystal fiber, wherein the handpiece allows an operator tocontrol the orientation of the output end to direct the radiation to atarget location of a patient.

Embodiments of the systems can include one or more of the followingfeatures and/or aspects of other aspects.

The handpiece can include an endoscope. The endoscope can include aflexible conduit and a portion of the photonic crystal fiber is threadedthrough a channel in the flexible conduit. The endoscope can include anactuator mechanically coupled to the flexible conduit configured to benda portion of the flexible conduit thereby allowing the operator to varythe orientation of the output end. The actuator can be configured tobend the portion of the flexible conduit so that the bent portion of theflexible conduit has a radius of curvature of about 12 centimeters orless (e.g., about 10 centimeters or less, about 8 centimeters or less,about 5 centimeters or less, about 3 centimeters or less). The actuatorcan be configured to bend the flexible conduit within a bend plane. Thehandpiece can be attached to the photonic crystal fiber to maintain anorientation of the dielectric confinement region to control theorientation of the photonic crystal fiber about its waveguide axiswithin the flexible conduit. The attachment between the handpiece andthe photonic crystal fiber can prevent twisting of the fiber by morethan about 10 degrees (e.g., by more than about 5 degrees) whilemaintaining operation. The endoscope can further include an auxiliaryconduit including a first portion coupled to the flexible conduit,wherein the photonic crystal fiber is threaded through a channel in theauxiliary conduit into the channel of the flexible conduit, theauxiliary conduit further comprising a second portion moveable withrespect to the first portion, wherein the photonic crystal fiber isattached to the second portion and moving the second portion allows theoperator to extend or retract the output end relative to an end of theflexible conduit. The second portion can extend or retract with respectto the first portion. The auxiliary conduit can be a rigid conduit.

In some embodiments, the handpiece includes a conduit and a portion ofthe photonic crystal fiber is threaded through the conduit. The conduitcan include a bent portion. The conduit can be formed from a deformablematerial. The handpiece can further include an actuator mechanicallycoupled to the conduit configured to bend a portion of the conduitthereby allowing the operator to vary the orientation of the output end.

The handpiece can include a tip extending past the output end thatprovides a minimum standoff distance of about 1 millimeter or morebetween the output end and the target location.

The photonic crystal fiber can be sufficiently flexible to guide theradiation to the target location while a portion of the photonic crystalfiber is bent through an angle of about 90 degrees or more and theportion has a radius of curvature of about 12 centimeters or less. Theradiation can have an average power at the output end of about 1 Watt ormore while the portion of the photonic crystal fiber is bent through anangle of about 90 degrees or more and the portion has a radius ofcurvature of about 12 centimeters or less. The radiation can have anaverage power at the output end of about 5 Watts or more while theportion of the photonic crystal fiber is bent through an angle of about90 degrees or more and the portion has a radius of curvature of about 12centimeters or less. The photonic crystal fiber can be sufficientlyflexible to guide the radiation to the target location while the portionof the photonic crystal fiber is bent through an angle of about 90degrees or more and the portion has a radius of curvature of about 10centimeters or less (e.g., about 5 centimeters or less).

The dielectric confinement region can include a layer of a firstdielectric material arranged in a spiral around the waveguide axis. Thedielectric confinement region can further include a layer of a seconddielectric material arranged in a spiral around the waveguide axis, thesecond dielectric material having a different refractive index from thefirst dielectric material. The first dielectric material can be a glass(e.g., a chalcogenide glass). The second dielectric material can be apolymer. The dielectric confinement region can include at least onelayer of a chalcogenide glass. The dielectric confinement region caninclude at least one layer of a polymeric material. In some embodiments,the dielectric confinement region includes at least one layer of a firstdielectric material extending along the waveguide axis and at least onelayer of a second dielectric material extending along the waveguideaxis, wherein the first and second dielectric materials can be co-drawnwith the first dielectric material.

The core can be a hollow core. The system can further include a fluidsource coupled to the input end or output end, wherein during operationthe fluid source supplies a fluid through the core. The fluid can be agas.

The core can have a diameter of about 1,000 microns or less (e.g., about500 microns or less). The photonic crystal fiber can have an outerdiameter of about 2,000 microns or less at the output end.

In some embodiments, the system further includes an optical waveguideand a connector that attaches the optical waveguide to the photoniccrystal fiber. The optical waveguide can be a second photonic crystalfiber. The system can also include a conduit surrounding the opticalwaveguide. The conduit can be more rigid than the optical waveguide. Thesystem can include a fluid source coupled to the conduit and whereinduring operation the fluid source supplies a fluid to the conduit.

The system can further include a laser to produce the radiation anddirect it towards the input end of the photonic crystal fiber. The lasercan be a CO₂ laser. The radiation can have a wavelength of about 2microns or more. In some embodiments, the radiation has a wavelength ofabout 10.6 microns.

In certain embodiments, the system further includes an auxiliaryradiation source and at least one additional fiber mechanically coupledto the photonic crystal fiber, the additional waveguide being configuredto deliver auxiliary radiation from the auxiliary radiation source tothe target location. The additional fiber can be mechanically coupled tothe photonic crystal fiber by the handpiece. The auxiliary radiationsource can be a second laser, different from the laser positioned todirect the radiation to the input end of the photonic crystal fiber. Thesecond laser can be an Nd:YAG laser, a diode laser, or a pulsed dyelaser. The auxiliary radiation can have a wavelength in the visibleportion of the electromagnetic spectrum.

At least a portion of the photonic crystal can be sterilized.

In general, in another aspect, the invention features articles thatinclude a length of a photonic crystal fiber, the photonic crystal fiberincluding a core extending along a waveguide axis and a dielectricconfinement region surrounding the core, the dielectric confinementregion being configured to guide radiation along the waveguide axis froman input end to an output end of the photonic crystal fiber, wherein thelength of the photonic crystal fiber is sterilized.

The articles can further include a sealed package containing the lengthof the photonic crystal fiber. Embodiments of the articles can includeone or more of the features of other aspects.

In general, in a further aspect, the invention features methods thatinclude directing radiation into an input end of a photonic crystalfiber and using a handpiece attached to the photonic crystal fiber tocontrol the orientation of an output end of the photonic crystal fiberand direct radiation emitted from the output end towards a targetlocation of a patient. Embodiments of the methods can include one ormore of the features of other aspects.

In general, in another aspect, the invention features methods thatinclude directing radiation to a target location of a patient through aphotonic crystal fiber, the photonic crystal fiber having a hollow coreand flowing a fluid through the hollow core to the target location ofthe patient.

Embodiments of the methods can include one or more of the followingfeatures and/or features of other aspects.

The radiation can have sufficient power to incise, excise, or ablatetissue at the target location. The fluid can have a sufficient pressureand temperature to coagulate blood at the target location.

The methods can include bending the photonic crystal fiber whiledirecting the radiation and the fluid to the target location. Bendingthe fiber can include bending a portion of the fiber through about 45°or more to have a radius of curvature of about 12 centimeters or less.

Directing the radiation and the fluid to the target location can includeholding a portion of a handpiece attached to the photonic crystal fiberand controlling the orientation of the output end using the handpiece.

The fluid can be a gas, a liquid, or a superfluid. In embodiments wherethe fluid is gas, the gas can have a pressure of about 0.5 PSI or more(e.g., about 1 PSI or more) at the output end. The gas can have atemperature of about 50° C. or more (e.g., about 80° C. or more) at thetarget location. The gas can be air. The gas can include carbon dioxide,oxygen, nitrogen, helium, neon, argon, krypton, or xenon. The gas can bea substantially pure gas. For example, the gas can include about 98% ormore of a single component gas. Alternatively, in some embodiments, thegas is gas mixture.

The fluid can be flowed into the hollow core at a rate of about 1 literper minute or more (e.g., about 2 liters per minute or more, about 5liters per minute or more, about 8 liters per minute or more).

The radiation can have a wavelength of about 2 microns or more (e.g.,about 10.6 microns). The radiation can have an average power of about 1Watt or more at the target location.

In general, in a further aspect, the invention features apparatus thatinclude a photonic crystal fiber including a core extending along awaveguide axis and a dielectric confinement region surrounding the core,the dielectric confinement region being configured to guide radiationalong the waveguide axis from an input end to an output end of thephotonic crystal fiber, and a sleeve coupled to the output end of thephotonic crystal fiber to allow the radiation to pass through the sleeveand exit the sleeve through a primary opening, the sleeve furthercomprising one or more secondary openings positioned so that gas flowedinto the sleeve exits the sleeve through the secondary openings.

Embodiments of the apparatus can include one or more of the followingfeatures and/or features of other aspects.

The gas flowed into the sleeve can exit the sleeve through the primaryopening in addition to through the secondary openings. The apparatus canfurther include a transparent element positioned between the primaryopening and the secondary openings that substantially transmits theradiation as it passes through the sleeve. The transparent element cansubstantially prevent gas from exiting the sleeve through the primaryopening. The transparent element can include Zinc Selenide (ZnSe).

The apparatus can further include a conduit positioned relative to thesecondary opening so that gas exiting the sleeve through the secondaryopening is drawn into an input end of the conduit.

The secondary opening can be positioned near to the primary opening. Theprimary opening can have a diameter that is smaller than an outerdiameter of the photonic crystal fiber at the output end. The apparatuscan further include a focusing element attached to the sleeve to focusthe radiation passing through the sleeve. Alternatively, oradditionally, the can include a reflecting element attached to thesleeve to reflect the radiation passing through the sleeve.

In general, in another aspect, the invention features apparatus thatinclude an assembly including a radiation input port configured toreceive radiation from a radiation source and an output port configuredto couple the radiation to a photonic crystal fiber, the assemblyfurther including a retardation element positioned to modify apolarization state of the radiation received from the radiation sourcebefore it is coupled to the photonic crystal fiber.

Embodiments of the apparatus can include one or more of the followingfeatures and/or features of other aspects.

The assembly can further include a gas input port configured to receivegas from a gas source. The photonic crystal fiber can have a hollowcore. The output port can be further configured to couple the gasreceived from the gas source into the hollow core of the photoniccrystal fiber. The apparatus can include the gas source.

The retardation element can be a reflective retardation element. Theapparatus can include the radiation source, wherein the radiation fromthe radiation source includes radiation having a wavelength γ. Thereflective retardation element can include a mirror and a retardationlayer having an optical thickness of about λ or less disposed on asurface of the mirror. The retardation layer can have an opticalthickness of about λ/4 along a direction about 45° relative to a normalto the surface of the mirror. λ can be about 2 microns or more. Forexample, λ can be about 10.6 microns.

The retardation element can be a transmissive retardation element.

The retardation element can modify the polarization state of theradiation from a substantially linear polarization state to asubstantially non-linear polarization state. The substantiallynon-linear polarization state can be a substantially circularpolarization state.

The assembly can further include a focusing element configured to focusthe radiation entering the assembly at the radiation input port to awaist near the output port.

The focusing element can focus the radiation to a waist diameter ofabout 1,000 microns or less (e.g., about 500 microns or less). Thefocusing element can be a lens. The lens can include ZnSe.

The apparatus can further include the photonic crystal fiber.

In general, in another aspect, the invention features methods thatinclude modifying a polarization state of radiation emitted from alaser, directing the radiation having the modified polarization stateinto an input end of a photonic crystal fiber having a hollow core, andcoupling gas from a gas source into the input end of the hollow core.

Embodiments of the methods can include one or more of the features orother aspects.

In general, in another aspect, the invention features methods thatinclude guiding radiation through an optical waveguide to tissue of apatient, wherein the optical waveguide has a hollow core, and directinggas to the tissue while guiding the radiation, wherein the radiation andgas are sufficient to cut (e.g., excise or ablate) the tissue and tosubstantially coagulate exposed blood.

In general, in a further aspect, the invention features a medical lasersystem, including a laser, an optical waveguide having a hollow core, adelivery device, a gas source (e.g., a cylinder of gas, a compressor, ablower) configured to deliver a gas to the tissue, wherein duringoperation radiation from the laser and gas from the gas source aredelivered to tissue of a patient, wherein the radiation and gas aresufficient to incise the tissue and substantially coagulate exposedblood.

In general, in another aspect, the invention features a system,including a laser having an output terminal, a photonic crystal fiberhaving an input end and an output end, the input end being configured toaccept radiation emitted from the output terminal, and a delivery devicefor allowing an operator to direct radiation emitted from the output endto target tissue.

In general, in another aspect, the invention features a system,including a CO₂ laser, an endoscope, and a photonic crystal fiber,wherein during operation the photonic crystal fiber guides radiationfrom the CO₂ laser through the endoscope to target tissue.

In general, in a further aspect, the invention features a coupler forcoupling gas and radiation into one end of a hollow core of a fiber.

Embodiments of the invention may include one or more of the followingfeatures.

The gas can be directed through the hollow core of the optical waveguideor the gas can be directed to the tissue through a tube separate fromthe hollow core. The radiation can be delivered from a laser (e.g., aCO₂ laser). The laser can have an output power of about 5 Watts or more(e.g., about 10 Watts or more, about 15 Watts or more, about 20 Watts ormore, about 50 Watts or more, about 100 Watts or more). The radiationdelivered to the tissue can have a power of about 1 Watt or more asmeasured at the distal end of the optical waveguide (e.g., about 2 Wattsor more, 5 Watts or more, 8 Watts or more, 10 Watts or more, about 20Watts or more, about 50 Watts or more). The radiation can have awavelength of about 10.6 microns. The gas can have a flow rate of about1 liter/min or more (e.g., about 2 liter/min or more, about 5 liter/minor more, about 8 liter/min or more, about 10 liter/min or more, about 12liter/min or more, about 15 liter/min or more, about 20 liter/min ormore).

The pressure of the gas exiting the hollow core can be relatively high.For example, the gas pressure exiting the fiber can correspond to a flowrate of about 1 liter/min or more (e.g., about 2 liter/min or more,about 5 liter/min or more, about 8 liter/min or more, about 10 liter/minor more, about 12 liter/min or more, about 15 liter/min or more, about20 liter/min or more) through a 1 meter length of fiber having a corediameter of about 500 μm.

The gas can include air, nitrogen, oxygen, carbon dioxide or a noble gas(e.g., He, Ne, Ar, Kr, and/or Xe). The gas can include substantiallyonly one compound (e.g., about 98% or more of one compound, about 99% ormore, about 99.5% or more, about 99.8% or more, about 99.9% or more).Alternatively, in some embodiments, the gas can include a mixture ofdifferent compounds (e.g., air).

The method can further include excising tissue with the radiation. Theoptical waveguide can be a photonic crystal fiber (e.g., a Bragg fiber).The gas can have a temperature of about 50° C. or more at the tissue(e.g., about 60° C. or more, about 70° C. or more, about 80° C. or more,about 90° C. or more, about 100° C. or more). The method can furtherinclude bending the fiber while delivering radiation to the tissue. Thefiber bend can have a radius of curvature of about 12 cm or less (e.g.,about 10 cm or less, about 8 cm or less, about 7 cm or less, about 6 cmor less, about 5 cm or less, about 4 cm or less, about 3 cm or less,about 2 cm or less).

A number of references are incorporated herein by reference. In case ofconflict, the present application will control.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features andadvantages of the invention will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a laser medical systemthat includes a photonic crystal fiber.

FIG. 2A is a cross-section view of an embodiment of a photonic crystalfiber.

FIG. 2B-2D are cross-sectional views of embodiments of confinementregions for photonic crystal fibers.

FIG. 3 is a cross-sectional view of a photonic crystal fiber including acladding having an asymmetric cross-section.

FIG. 4A-4D are cross-sectional views of embodiments of sleeves attachedto an output end of a photonic crystal fiber.

FIGS. 5A and 5B are diagrams of embodiments of coupling assemblies forcoupling radiation and a fluid into a hollow core of a photonic crystalfiber.

FIG. 6 is a diagram of a handpiece that includes a malleable conduit.

FIG. 7A is a schematic diagram of another embodiment of a laser medicalsystem including a photonic crystal fiber.

FIG. 7B is a diagram of an endoscope.

FIG. 7C is a schematic diagram of a further embodiment of a medicallaser system including a photonic crystal fiber.

FIG. 8 is a schematic diagram of a portion of a medical laser systemthat includes a photonic crystal fiber and a second fiber waveguide.

FIG. 9 is a schematic diagram of a portion of a medical laser systemthat includes a photonic crystal fiber and a tube for exhausting fluidfrom the fiber.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1, a medical laser system 100 includes a CO₂ laser110, and a photonic crystal fiber 120 having a hollow core to guideradiation 112 from the laser to a target location 99 of a patient.Radiation 112 has a wavelength of 10.6 microns. Laser radiation 112 iscoupled by a coupling assembly 130 into the hollow core of photoniccrystal fiber 120, which delivers the radiation through a handpiece 140to target location 99. During use, an operator (e.g., a medicalpractitioner, such as a surgeon, a dentist, an ophthalmologist, or aveterinarian) grips a portion 142 of handpiece 140, and manipulates thehandpiece to direct laser radiation 113 emitted from an output end ofphotonic crystal fiber 120 to target location 99 in order to perform atherapeutic function at the target location. For example, the radiationcan be used to excise, incise, ablate, or vaporize tissue at the targetlocation.

CO₂ laser 110 is controlled by an electronic controller 150 for settingand displaying operating parameters of the system. The operator controlsdelivery of the laser radiation using a remote control 152, such as afoot pedal. In some embodiments, the remote control is a component ofhandpiece 140, allowing the operator to control the direction of emittedlaser radiation and delivery of the laser radiation with one hand orboth hands.

In addition to grip portion 142, handpiece 140 includes a stand off tip144, which maintains a desired distance (e.g., from about 0.1millimeters to about 30 millimeters) between the output end of fiber 120and target tissue 99. The stand off tip assist the operator inpositioning the output end of photonic crystal fiber 120 from targetlocation 99, and can also reduce clogging of the output end due todebris at the target location. In some embodiments, handpiece 140includes optical components (e.g., a lens or lenses), which focus thebeam emitted from the fiber to a desired spot size. The waist of thefocused beam can be located at or near the distal end of the stand offtip.

In some embodiments, fiber 120 can be easily installed and removed fromcoupling assembly 130, and from handpiece 140 (e.g., using conventionalfiber optic connectors). This can facilitate ease of use of the systemin single-use applications, where the fiber is replaced after eachprocedure.

Typically, CO₂ laser 110 has an average output power of about 5 Watts toabout 80 Watts at 10.6 microns (e.g., about 10 Watts or more, about 20Watts or more). In many applications, laser powers of about 5 Watts toabout 30 Watts are sufficient for the system to perform its intendedfunction. For example, where system 100 is being used to excise orincise tissue, the radiation is confined to a small spot size and alaser having an average output power in this range is sufficient.

In certain embodiments, however, laser 110 can have an output power ashigh as about 100 Watts or more (e.g., up to about 500 Watts). Forexample, in applications where system 100 is used to vaporize tissueover a relatively large area (e.g., several square millimeters orcentimeters), extremely high power lasers may be desirable.

Photonic crystal fiber can deliver the radiation from laser 110 to thetarget location with relatively high efficiency. For example, the fiberaverage output power can be about 50% or more of the fiber input energy(e.g., about 60% or more, about 70% or more, about 80% or more).Accordingly, the fiber's output power can be about 3 Watts or more(e.g., about 8 Watts or more, about 10 Watts or more, about 15 Watts ormore). In certain embodiments, however, the average output power fromthe fiber can be less than 50% of the laser power, and still besufficiently high to perform the intended procedure. For example, insome embodiments, the fiber average output power can be from about 20%to about 50% of the laser average output power.

The length of photonic crystal fiber 120 can vary as desired. In someembodiments, the fiber is about 1.2 meters long or more (e.g., about 1.5meters or more, about 2 meters or more, about 3 meters or more, about 5meters or more). The length is typically dependent on the specificapplication for which the laser system is used. In applications wherelaser 110 can be positioned close to the patient, and/or where the rangeof motion of the handpiece desired for the application is relativelysmall, the length of the fiber can be relatively short (e.g., about 1.5meters or less, about 1.2 meters or less, about 1 meter or less). Incertain applications, the length of fiber 120 can be very short (e.g.,about 50 centimeters or less, about 20 centimeters or less, about 10centimeters or less). For example, very short lengths of photoniccrystal fiber may be useful in procedures where the system can deliverradiation from the laser to the fiber by some other means (e.g., adifferent waveguide or an articulated arm). Very short fiber lengths maybe useful for nose and ear procedures, for example.

However, in applications where it is inconvenient for the laser to beplaced in close proximity to the patient and/or where a large range ofmotion of the handpiece is desired, the length of the fiber is longer(e.g., about 2 meters or more, about 5 meters or more, about 8 meters ormore). For example, in surgical applications, where a large team ofmedical practitioners is needed in close proximity to the patient, itmay be desirable to place the laser away from the operating table (e.g.,in the corner of the operating room, or in a different room entirely).In such situations, a longer fiber may be desirable.

In general, photonic crystal fiber 120 is flexible, and can be bent torelatively small radii of curvature over relatively large angles withoutsignificantly impacting its performance (e.g., without causing the fiberto fail, or without reducing the fiber transmission to a level where thesystem cannot be used for its intended use while the fiber is bent). Insome embodiments, an operator can bend photonic crystal fiber 120 tohave a relatively small radius of curvature, such as about 15 cm or less(e.g., about 10 cm or less, about 8 cm or less, about 5 cm or less,about 3 cm or less) while still delivering sufficient power to thetarget location for the system to perform its function.

In general, the angle through which the fiber is bent can vary, andusually depends on the procedure being performed. For example, in someembodiments, the fiber can be bent through about 90° or more (e.g.,about 120° or more, about 150° or more).

Losses of transmitted power due to the operator bending photonic crystalfiber 120 may be relatively small. In general, losses due to bendsshould not significantly damage the fiber, e.g., causing it to fail, orreduce the fiber output power to a level where the system can no longerperform the function for which it is designed. Embodiments of photoniccrystal fiber 120 (e.g., about 1 meter or more in length) can be bentthrough 90° with a bend radius of about 5 centimeters or less, and stilltransmit about 30% or more (e.g., about 50% or more, about 70% or more)of radiation coupled into the fiber at the guided wavelength. Thesefibers can provide such transmission characteristics and provide averageoutput power of about 3 Watts or more (e.g., about 5 Watts or more,about 8 Watts or more, about 10 Watts or more).

The quality of the beam of the laser radiation emitted from the outputend of fiber 120 can be relatively good. For example, the beam can havea low M² value, such as about 4 or less (e.g., about 3 or less, about2.5 or less, about 2 or less). M² is a parameter commonly used todescribe laser beam quality, where an M² value of about 1 corresponds toa TEM₀₀ beam emitted from a laser, which has a perfect Gaussian profile.The M² value is related to the minimum spot size that can be formed fromthe beam according to the formula:d _(s)=1.27fλM ² /d _(b)  (1)where d_(s) is the minimum spot diameter, d_(b) is the beam diameterprior to being focused to the spot by a lens having focal length f.Accordingly, the minimum possible spot size a beam can be focused isproportional to the M² value for the beam. Practically, beams havingsmaller values of M² can provide higher radiation power densities to thetarget area, with less damage to surrounding tissue due to the decreasedspot size.

The spot size of radiation delivered by photonic crystal fiber 120 tothe target tissue can be relatively small. For example, in certainembodiments, the spot can have a diameter of about 500 microns or less(e.g., about 300 microns or less, about 200 microns or less, such asabout 100 microns) at a desired working distance from the fiber's outputend (e.g., from about 0.1 mm to about 3 mm). As discussed previously, asmall spot size is desirable where system 100 is being used to excise orincise tissue or in other applications where substantial precision inthe delivery of the radiation is desired. Alternatively, in applicationswhere tissue is to be ablated or vaporized, and/or a lesser level ofprecision is sufficient, the spot size can be relatively large (e.g.,having a diameter of about 2 millimeters or more, about 3 millimeters ormore, about 4 millimeters or more).

While laser 110 is a CO₂ laser, photonic crystal fibers can be used inmedical laser systems that use other types or lasers, operating atwavelengths different from 10.6 microns. In general, medical lasersystems can provide radiation at ultraviolet (UV), visible, or infrared(IR) wavelengths. Lasers delivering IR radiation, for example, emitradiation having a wavelength between about 0.7 microns and about 20microns (e.g., between about 2 to about 5 microns or between about 8 toabout 12 microns). Waveguides having hollow cores, such as photoniccrystal fiber 120, are well-suited for use with laser systems havingwavelengths of about 2 microns or more, since gases that commonly occupythe core have relatively low absorptions at these wavelengths comparedto many dielectric materials (e.g., silica-based glasses and variouspolymers). In addition to CO₂ lasers, other examples of lasers which canemit IR radiation include Nd:YAG lasers (e.g., at 1.064 microns), Er:YAGlasers (e.g., at 2.94 microns), Er, Cr: YSGG (Erbium, Chromium dopedYttrium Scandium Gallium Garnet) lasers (e.g., at 2.796 microns), Ho:YAGlasers (e.g., at 2.1 microns), free electron lasers (e.g., in the 6 to 7micron range), and quantum cascade lasers (e.g., in the 3 to 5 micronrange).

In general, the type of laser used in a medical laser system depends onthe purpose for which the system is designed. The type of laser can beselected depending on whether the system is to be used in surgicalprocedures, in diagnosis, or in physiologic studies. For example, anargon laser, which delivers in the blue and green regions of the visiblelight spectrum, with two energy peaks, at 488 nm and 514 nm, can be usedfor photocoagulation. A dye laser, which is a laser with organic dyedissolved in a solvent as the active medium whose beam is in the visiblelight spectrum, can be used in photodynamic therapy. Excimer lasersprovide radiation in the ultraviolet spectrum, penetrates tissues only asmall distance, can be used to break chemical bonds of molecules intissue instead of generating heat to destroy tissue. Such lasers can beused in ophthalmological procedures and laser angioplasty. Ho:YAG laserscan provide radiation in the near infrared spectrum and can be used forphotocoagulation and photoablation. Krypton lasers provide radiation inthe yellow-red visible light spectrum, and can be used forphotocoagulation. Radiation from KTP lasers can be frequency-doubled toprovide radiation in the green visible light spectrum and can be usedfor photoablation and photocoagulation. Nd:YAG lasers can be forphotocoagulation and photoablation. Pulsed dye lasers can be used toprovide in the yellow visible light spectrum (e.g., with a wavelength of577 nm or 585 nm), with alternating on and off phases of a fewmicroseconds each, and can be used to decolorize pigmented lesions.

In general, laser systems can use continuous wave or pulsed lasers.Furthermore, while CO₂ lasers are typically used at average outputpowers of about 5 Watts to about 100 Watts, photonic crystal fibers cangenerally be used with a variety of laser powers. For example, averagelaser power can be in the milliwatt range in certain systems, up to asmuch as several hundred Watts (e.g., about 200 Watts or more) inextremely high power systems.

In general, for high power systems, the average power density guided byfiber 120 can be extremely high. For example, power density in thefiber, or exiting the fiber's core, can be about 10³ W/cm² or more(e.g., about 10⁴ W/cm² or more, about 10⁵ W/cm² or more, 10⁶ W/cm² ormore).

Referring to FIG. 2A, in general, photonic crystal fiber 120 includes acore 210, which is surrounded by a confinement region 220 extendingalong a waveguide axis 299 (normal to the plane of FIG. 2A). Confinementregion 220 is surrounded by a cladding 230 (e.g., a polymer cladding),which provides mechanical support and protects the core and confinementregion from environmental hazards. Confinement region 220 includes aphotonic crystal structure that substantially confines radiation at awavelength λ to core 210. Examples of such structures are described withreference to FIGS. 2B-2D below. As used herein, a photonic crystal is astructure (e.g., a dielectric structure) with a refractive indexmodulation (e.g., a periodic refractive index modulation) that producesa photonic bandgap in the photonic crystal. An example of such astructure, giving rise to a one dimensional refractive index modulation,is a stack of dielectric layers of high and low refractive index, wherethe layers have substantially the same optical thickness. A photonicbandgap, as used herein, is a range of frequencies in which there are noaccessible extended (i.e., propagating, non-localized) states in thedielectric structure. Typically the structure is a periodic dielectricstructure, but it may also include, e.g., more complex “quasi-crystals.”The bandgap can be used to confine, guide, and/or localize light bycombining the photonic crystal with “defect” regions that deviate fromthe bandgap structure. Moreover, there are accessible extended statesfor frequencies both below and above the gap, allowing light to beconfined even in lower-index regions (in contrast to index-guided TIRstructures). The term “accessible” states means those states with whichcoupling is not already forbidden by some symmetry or conservation lawof the system. For example, in two-dimensional systems, polarization isconserved, so only states of a similar polarization need to be excludedfrom the bandgap. In a waveguide with uniform cross-section (such as atypical fiber), the wavevector β is conserved, so only states with agiven β need to be excluded from the bandgap to support photonic crystalguided modes. Moreover, in a waveguide with cylindrical symmetry, the“angular momentum” index m is conserved, so only modes with the same mneed to be excluded from the bandgap. In short, for high-symmetrysystems the requirements for photonic bandgaps are considerably relaxedcompared to “complete” bandgaps in which all states, regardless ofsymmetry, are excluded.

Theoretically, a photonic crystal is only completely reflective in thebandgap when the index modulation in the photonic crystal has aninfinite extent. Otherwise, incident radiation can “tunnel” through thephotonic crystal via an evanescent mode that couples propagating modeson either side of the photonic crystal. In practice, however, the rateof such tunneling decreases exponentially with photonic crystalthickness (e.g., the number of alternating layers). It also decreaseswith the magnitude of the index contrast in the confinement region.

Furthermore, a photonic bandgap may extend over only a relatively smallregion of propagation vectors. For example, a dielectric stack may behighly reflective for a normally incident ray and yet only partiallyreflective for an obliquely incident ray. A “complete photonic bandgap”is a bandgap that extends over all possible wavevectors and allpolarizations. Generally, a complete photonic bandgap is only associatedwith a photonic crystal having index modulations along three dimensions.However, in the context of EM radiation incident on a photonic crystalfrom an adjacent dielectric material, we can also define an“omnidirectional photonic bandgap,” which is a photonic bandgap for allpossible wavevectors and polarizations for which the adjacent dielectricmaterial supports propagating EM modes. Equivalently, an omnidirectionalphotonic bandgap can be defined as a photonic band gap for all EM modesabove the light line, wherein the light line defines the lowestfrequency propagating mode supported by the material adjacent thephotonic crystal. For example, in air the light line is approximatelygiven by ω=cβ, where ω is the angular frequency of the radiation, β isthe wavevector, and c is the speed of light. A description of anomnidirectional planar reflector is disclosed in U.S. Pat. No.6,130,780, the entire contents of which are incorporated herein byreference. Furthermore, the use of alternating dielectric layers toprovide omnidirectional reflection (in a planar limit) for a cylindricalwaveguide geometry is disclosed in Published PCT application WO00/22466, the contents of which are incorporated herein by reference.

When confinement region 220 gives rise to an omnidirectional bandgapwith respect to core 210, the guided modes are strongly confinedbecause, in principle, any EM radiation incident on the confinementregion from the core is completely reflected. As described above,however, such complete reflection only occurs when there are an infinitenumber of layers. For a finite number of layers (e.g., about 20 layers),an omnidirectional photonic bandgap may correspond to a reflectivity ina planar geometry of at least 95% for all angles of incidence rangingfrom 0° to 80° and for all polarizations of EM radiation havingfrequency in the omnidirectional bandgap. Furthermore, even when fiber120 has a confinement region with a bandgap that is not omnidirectional,it may still support a strongly guided mode, e.g., a mode with radiationlosses of less than 0.1 dB/km for a range of frequencies in the bandgap.Generally, whether or not the bandgap is omnidirectional will depend onthe size of the bandgap produced by the alternating layer (whichgenerally scales with index contrast of the two layers) and thelowest-index constituent of the photonic crystal.

Regarding the structure of photonic crystal fiber 120, in general, thediameter of core 210 (indicated by reference numeral 211 in FIG. 2A) canvary depending on the end-use application of system 100. For example,where a large spot size is desired, the core can be relatively large(e.g., about 1 mm or more, about 2 mm or more). Alternatively, when asmall spot size is desired, core diameter 211 can be much smaller (e.g.,about 500 microns or less, about 300 microns or less, about 200 micronsor less, about 100 microns or less).

More generally, where fiber 120 is used in systems with other types oflaser, and/or used to guide wavelengths other than 10.6 microns, thecore diameter depends on the wavelength or wavelength range of theenergy to be guided by the fiber, and on whether the fiber is a singleor multimode fiber. For example, where the fiber is a single mode fiberfor guiding visible wavelengths (e.g., between about 400 nm and about800 nm) the core radius can be in the sub-micron to several micron range(e.g., from about 0.5 microns to about 5 microns). However, the coreradius can be in the tens to thousands of microns range (e.g., fromabout 10 microns to about 2,000 microns, such as about 500 microns toabout 1,000 microns), for example, where the fiber is a multimode fiberfor guiding IR wavelengths. The core radius can be about 5λ or more(e.g., about 10λ or more, about 20λ or more, about 50λ or more, about100λ or more), where λ is the wavelength of the guided energy.

An advantage of photonic crystal fibers is that fibers having small corediameters can be readily produced since fibers can be drawn from aperform, preserving the relative proportions of the fiber'scross-sectional structure while reducing the dimensions of thatstructure to small sizes in a controlled manner.

In photonic crystal fiber 120, core 220 is hollow. Alternatively, inembodiments where there are no fluids pumped through the core, core 220can include any material or combination of materials that areTheologically compatible with the materials forming confinement region220 and that have sufficiently high transmission properties at theguided wavelength(s). In some embodiments, core 220 includes adielectric material (e.g., an amorphous dielectric material), such as aninorganic glass or a polymer. In certain embodiments, core 220 caninclude one or more dopant materials, such as those described in U.S.patent application Ser. No. 10/121,452, entitled “HIGH INDEX-CONTRASTFIBER WAVEGUIDES AND APPLICATIONS,” filed Apr. 12, 2002 and nowpublished under Pub. No. US-2003-0044158-A1, the entire contents ofwhich are hereby incorporated by reference.

Cladding 230 can be formed from a polymer (e.g., an acrylate or siliconepolymer) or other material. Cladding 230 can be formed from a materialthat is also used to as part of confinement region 220, which aredescribed below. In applications where the cladding comes in contactwith a patient, it can be formed from materials that conform to FDAstandards for medical devices. In these instances, silicone polymers,for example, may be particularly suited for use as the claddingmaterial. Typically, cladding 230 protects the fiber from externaldamage. By selecting the appropriate thickness, composition, and/orstructure, cladding 230 can also be designed to limit the flexibility ofthe fiber, e.g., to prevent damage by small radius of curvature bends.

In general, the thickness of fiber 120 can vary. The thickness isindicated by outer diameter (OD) 231 in FIG. 2A. OD 231 can be selectedso that fiber 120 is compatible with other pieces of equipment. Forexample, fiber 120 can be made so that OD 231 is sufficiently small sothat the fiber can be threaded through a channel in an endoscope orother tool (e.g., OD 231 can be about 2,000 microns or less). In someembodiments, fiber 120 has a relatively small OD (e.g., about 1,000microns or less). Narrow fibers can be useful in applications where theyare to be inserted into narrow spaces, such as through a patient'surethra. Alternatively, in some embodiments, diameter 231 can berelatively large compared (e.g., about 3,000 microns or more). LargeOD's can reduce the mechanical flexibility of the fiber, which canprevent the fiber from bending to small radii of curvature that damagethe fiber or reduce its transmission to a level where the system can nolonger perform its intended function.

In addition to cladding 230, fiber 200 may include additional componentsto limit bend radii. For example, the fiber may include a spirally woundmaterial around its outer diameter (e.g., a spirally wound wire).Alternatively, or additionally, the fiber may include additionalcladdings to provide additional mechanical support.

Although the fiber can be bent (as discussed above), in someembodiments, the fiber may be constrained from bending to radii ofcurvature of less than about 20 cm (e.g., about 10 cm or less, 8 cm orless, 5 cm or less) during regular use in the application for which itis designed.

The cladding material may be selected so that the fiber is sterilizable.For example, the cladding material may be selected so that the fiber canwithstand high temperatures (e.g., those experienced in an autoclave).

Turning to the structure and composition of confinement region 220, insome embodiments, photonic crystal fiber 120 is a Bragg fiber andconfinement region 220 includes multiple alternating layers having highand low refractive indexes, where the high and low index layers havesimilar optical thickness. For example, referring to FIG. 2B, in someembodiments, confinement region 220A includes multiple annulardielectric layers of differing refractive index (i.e., layers composedof a high index material having a refractive index n_(H), and layerscomposed of a low index material having a refractive index n_(L)),indicated as layers 212, 213, 214, 215, 216, 217, 218, 219, 222, and223. Here, n_(H)>n_(L) and n_(H)−n_(L) can be, for example, about 0.01or more, about 0.05 or more, about 0.1 or more, about 0.2 or more, about0.5 or more. For convenience, only a few of the dielectric confinementlayers are shown in FIG. 2B. In practice, confinement region 220A mayinclude many more layers (e.g., about 15 layers or more, about 20 layersor more, about 30 layers or more, about 40 layers or more, about 50layers or more, about 80 layers or more).

In some embodiments, confinement region 220 can give rise to anomnidirectional bandgap with respect to core 210, wherein the guidedmodes are strongly confined because, in principle, any EM radiationincident on the confinement region from the core is completelyreflected. However, such complete reflection only occurs when there arean infinite number of layers. For a finite number of layers (e.g., about20 layers), an omnidirectional photonic bandgap may correspond to areflectivity in a planar geometry of at least 95% for all angles ofincidence ranging from 0° to 80° and for all polarizations of EMradiation having frequency in the omnidirectional bandgap. Furthermore,even when fiber 120 has a confinement region with a bandgap that is notomnidirectional, it may still support a strongly guided mode, e.g., amode with radiation losses of less than 0.1 dB/km for a range offrequencies in the bandgap. Generally, whether or not the bandgap isomnidirectional will depend on the size of the bandgap produced by thealternating layers (which generally scales with index contrast of thetwo layers) and the lowest-index constituent of the photonic crystal.

The existence of an omnidirectional bandgap, however, may not benecessary for useful application of fiber 120. For example, in someembodiments, a laser beam used to establish the propagating field in thefiber is a TEM₀₀ mode. This mode can couple with high efficiency to theHE₁₁ mode of a suitably designed fiber. Thus, for successful applicationof the fiber for transmission of laser energy, it may only be necessarythat the loss of this one mode be sufficiently low. More generally, itmay be sufficient that the fiber support only a number of low loss modes(e.g., the HE₁₁ mode and the modes that couple to it from simpleperturbations, such as bending of the fiber). In other words, photonicbandgap fibers may be designed to minimize the losses of one or a groupof modes in the fiber, without necessarily possessing an omnidirectionalbandgap.

For a planar dielectric reflector, it is well-known that, for normalincidence, a maximum band gap is obtained for a “quarter-wave” stack inwhich each layer has equal optical thickness λ/4, or equivalentlyn_(hi)d_(hi)=n_(lo)d_(lo)=λ/4, where d_(hi/lo) and n_(hi/lo) refer tothe thickness and refractive index, respectively, of high-index andlow-index layers in the stack. Normal incidence, however, corresponds toβ=0, whereas for a cylindrical waveguide the desired modes typically lienear the light line ω=cβ (in the limit of large R, the lowest-ordermodes are essentially plane waves propagating along z-axis, i.e., thewaveguide axis). In this case, the quarter-wave condition becomes:d _(hi)√{square root over (n _(hi) ²−1)}=d _(lo)√{square root over (n_(lo) ²−1)}=λ/4  (2)

This equation may not be exactly optimal because the quarter-wavecondition is modified by the cylindrical geometry, which may require theoptical thickness of each layer to vary smoothly with its radialcoordinate. In addition, the differing absorption of the high and lowindex materials can change the optimal layer thicknesses from theirquarter-wave values.

In certain embodiments, confinement region 220 includes layers that donot satisfy the quarter-wave condition given in Eq. 2. In other words,for the example shown in FIG. 2B, one or more of layers 212, 213, 214,215, 216, 217, 218, 219, 222, and 223 are thicker or thinner thand_(λ/4), where

${d_{\lambda/4} = \frac{\lambda}{4\sqrt{n^{2} - 1}}},$and n is the refractive index of the layer (i.e., d_(λ/4) corresponds toan optical thickness equal to the quarter-wave thickness). For example,one or more layers in the confinement region can have a thickness ofabout 0.9 d_(λ/4) or less (e.g., about 0.8 d_(λ/4) or less, about 0.7d_(λ/4) or less, about 0.6 d_(λ/4) or less, about 0.5 d_(λ/4) or less,about 0.4 d_(λ/4) or less, about 0.3 d_(λ/4) or less), or about 1.1d_(λ/4) or more (e.g., about 1.2 d_(λ/4) or more, about 1.3 d_(λ/4) ormore, about 1.4 d_(λ/4) or more, about 1.5 d_(λ/4) or more, about 1.8d_(λ/4) or more, about 2.0 d_(λ/4) or more). In some embodiments, alllayers in the confinement region can be detuned from the quarter-wavecondition. In some embodiments, the thickness of one or more of the highindex layers can be different (e.g., thicker or thinner) from thethickness of the other high index layers. For example, the thickness ofthe innermost high index layer can be different from the thickness ofthe other high index layers. Alternatively, or additionally, thethickness of one or more of the low index layers can be different (e.g.,thicker or thinner) from the thickness of the other low index layers.For example, the thickness of the innermost low index layer can bedifferent from the thickness of the other low index layers.

Detuning the thickness of layers in the confinement region from thequarter-wave condition can reduce the attenuation of photonic crystalfiber 120 compared to a test fiber, which refers to a fiber identical tophotonic crystal fiber 120, except that the quarter-wave condition issatisfied for all layers in the confinement region (i.e., the test fiberhas an identical core, and its confinement region has the same number oflayers with the same composition as photonic crystal fiber 120). Forexample, fiber 120 can have an attenuation for one or more guided modesthat is reduced by a factor of about two or more compared to theattenuation of the test fiber (e.g., reduced by a factor of about threeor more, about four or more, about five or more, about ten or more,about 20 or more, about 50 or more, about 100 or more). Examples ofphotonic crystal fibers illustrating reduce attenuation are described inU.S. patent application Ser. No. 10/978,605, entitled “PHOTONIC CRYSTALWAVEGUIDES AND SYSTEMS USING SUCH WAVEGUIDES,” filed on Nov. 1, 2004,the entire contents of which is hereby incorporated by reference.

The thickness of each layer in the confinement region can vary dependingon the composition and structure of the photonic crystal fiber.Thickness can also vary depending on the wavelength, mode, or group ofmodes for which the photonic crystal fiber is optimized. The thicknessof each layer can be determined using theoretical and/or empiricalmethods. Theoretical methods include computational modeling. Onecomputational approach is to determine the attenuation of a fiber fordifferent layer thicknesses and use an optimization routine (e.g., anon-linear optimization routine) to determine the values of layerthickness that minimize the fiber's attenuation for a guided mode. Forexample, the “downhill simplex method”, described in the text NumericalRecipes in FORTRAN (second edition), by W. Press, S. Teukolsky, W.Vetterling, and B Flannery, can be used to perform the optimization.

Such a model should account for different attenuation mechanisms in afiber. Two mechanisms by which energy can be lost from a guided EM modeare by absorption loss and radiation loss. Absorption loss refers toloss due to material absorption. Radiation loss refers to energy thatleaks from the fiber due to imperfect confinement. Both modes of losscontribute to fiber attenuation and can be studied theoretically, forexample, using transfer matrix methods and perturbation theory. Adiscussion of transfer matrix methods can be found in an article by P.Yeh et al., J. Opt. Soc. Am., 68, p. 1196 (1978). A discussion ofperturbation theory can found in an article by M. Skorobogatiy et al.,Optics Express, 10, p. 1227 (2002). Particularly, the transfer matrixcode finds propagation constants β for the “leaky” modes resonant in aphotonic crystal fiber structure. Imaginary parts of β's define themodal radiation loss, thus Loss_(radiation)˜Im(β). Loss due to materialabsorption is calculated using perturbation theory expansions, and interms of the modal field overlap integral it can be determined from

$\begin{matrix}{{{Loss}_{absorption} \sim {2{\pi\omega}{\int_{0}^{\infty}{r\ {\mathbb{d}{r\left( {\alpha{\overset{\rightharpoonup}{E}}_{\beta}^{*}\overset{\rightharpoonup}{E}} \right)}}}}}},} & (3)\end{matrix}$where ω is the radiation frequency, r is the fiber radius, a is bulkabsorption of the material, and {right arrow over (E)}_(β) is anelectric field vector.

Alternatively, the desired mode fields that can propagate in the fibercan be expanded in a suitable set of functions, such as B-splines (see,e.g., A Practical Guide to Splines, by C. deBoor). Application of theGalerkin conditions (see, e.g., Computational Galerkin Methods, C. A. J.Fletcher, Springer-Verlag, 1984) then converts Maxwell's equations intoa standard eigenvalue-eigenvector problem, which can be solved using theLAPACK software package (freely available, for example, from the netlibrepository on the internet, at “http://www.netlib.org”). The desiredcomplex propagation constants, containing both material and radiationlosses, are obtained directly from the eigenvalues.

Guided modes can be classified as one of three types: pure transverseelectric (TE); pure transverse magnetic (TM); and mixed modes. Lossoften depends on the type of mode. For example, TE modes can exhibitlower radiation and absorption losses than TM/mixed modes. Accordingly,the fiber can be optimized for guiding a mode that experiences lowradiation and/or absorption loss.

While confinement region 220A includes multiple annular layers that giverise to a radial refractive index modulation, in general, confinementregions can also include other structures to provide confinementproperties. For example, referring to FIG. 2C, a confinement region 220Bincludes continuous layers 240 and 250 of dielectric material (e.g.,polymer, glass) having different refractive indices, as opposed tomultiple discrete, concentric layers. Continuous layers 240 and 250 forma spiral around axis 299. One or more of the layers, e.g., layer 240 isa high-index layer having an index n_(H) and a thickness d_(H), and thelayer, e.g., layer 250, is a low-index layer having an index n_(L) and athickness d_(L), where n_(H)>n_(L) (e.g., n_(H)−n_(L) can be about 0.01or more, about 0.05 or more, about 0.1 or more, about 0.2 or more, about0.5 or more).

Because layers 240 and 250 spiral around axis 199, a radial sectionextending from axis 199 intersects each of the layers more than once,providing a radial profile that includes alternating high index and lowindex layers.

The spiraled layers in confinement region 220B provide a periodicvariation in the index of refraction along a radial section, with aperiod corresponding to the optical thickness of layers 240 and 250. Ingeneral, the radial periodic variation has an optical periodcorresponding to n₂₄₀d₂₄₀+n₂₅₀d₂₅₀.

The thickness (d₂₄₀ and d₂₅₀) and optical thickness (n₂₄₀d₂₄₀ andn₂₅₀d₂₅₀) of layers 240 and 250 are selected based on the sameconsiderations as discussed for confinement region 220A above.

For the embodiment shown in FIG. 2C, confinement region 220B is 5optical periods thick. In practice, however, spiral confinement regionsmay include many more optical periods (e.g., about 8 optical periods ormore, about 10 optical periods or more, about 15 optical periods ormore, about 20 optical periods or more, about 25 optical periods ormore, such as about 40 or more optical periods).

Fiber's having spiral confinement regions can be formed from a spiralperform by rolling a planar multilayer film into a spiral andconsolidating the spiral by fusing (e.g., by heating) the adjacentlayers of the spiral together. In some embodiments, the planarmultilayer film can be rolled into a spiral around a mandrel (e.g., aglass cylinder or rod), and the mandrel can be removed (e.g., by etchingor by separating the mandrel from the spiral sheath and slipping it outof the sheath) after consolidation to provide the spiral cylinder. Themandrel can be formed from a single material, or can include portions ofdifferent materials. For example, in some embodiments, the mandrel canbe coated with one or more layers that are not removed afterconsolidation of the rolled spiral structure. As an example, a mandrelcan be formed from a first material (e.g., a silicate glass) in the formof a hollow rod, and a second material (e.g., another glass, such as achalcogenide glass) coated onto the outside of the hollow rod. Thesecond material can be the same as one of the materials used to form themultilayer film. After consolidation, the first material is etched, andthe second material forms part of the fiber preform.

In some embodiments, additional material can be disposed on the outsideof the wrapped multilayer film. For example, a polymer film can bewrapped around the outside of the spiral, and subsequently fused to thespiral to provide an annular polymer layer (e.g., the cladding). Incertain embodiments, both the multilayer film and an additional film canbe wrapped around the mandrel and consolidated in a single fusing step.In embodiments, the multilayer film can be wrapped and consolidatedaround the mandrel, and then the additional film can be wrapped aroundthe fused spiral and consolidated in a second fusing step. The secondconsolidation can occur prior to or after etching the mandrel.Optionally, one or more additional layers can be deposited (e.g., usingCVD) within the spiral prior to wrapping with the additional film.

Methods for preparing spiral articles are described in U.S. patentapplication Ser. No. 10/733,873, entitled “FIBER WAVEGUIDES AND METHODSOF MAKING SAME,” filed on Dec. 10, 2003, the entire contents of whichare hereby incorporated by reference.

Referring to FIG. 2D, in some embodiments, photonic crystal fiber 120can include a confinement region 220C that includes a spiral portion 260and an annular portion 270. The number of layers in annular portion 270and spiral portion 260 (along a radial direction from the fiber axis)can vary as desired. In some embodiments, annular portion can include asingle layer. Alternatively, as shown in FIG. 2D, annular portion 270can include multiple layers (e.g., two or more layers, three or morelayers, four or more layers, five or more layers, ten or more layers).

In embodiments where annular portion 270 includes more than one layer,the optical thickness of each layer may be the same or different asother layers in the annular portion. In some embodiments, one or more ofthe layers in annular portion 270 may have an optical thicknesscorresponding to the quarter wave thickness (i.e., as given by Eq. (2).Alternatively, or additionally, one or more layers of annular portion270 can have a thickness different from the quarter wave thickness.Layer thickness can be optimized to reduce (e.g., minimize) attenuationof guided radiation using the optimization methods disclosed herein.

In certain embodiments, annular portion 270 can be formed from materialsthat have relatively low concentrations of defects that would scatterand/or absorb radiation guided by photonic crystal fiber 120. Forexample, annular portion 270 can include one or more glasses withrelatively low concentrations of inhomogeneities and/or impurities.Inhomogeneities and impurities can be identified using optical orelectron microscopy, for example. Raman spectroscopy, glow dischargemass spectroscopy, sputtered neutrals mass spectroscopy or FourierTransform Infrared spectroscopy (FTIR) can also be used to monitorinhomogeneities and/or impurities in photonic crystal fibers.

In certain embodiments, annular portion 270 is formed from materialswith a lower concentration of defects than spiral portion 260. Ingeneral, these defects include both structural defects (e.g.,delamination between layers, cracks) and material inhomogeneities (e.g.,variations in chemical composition and/or crystalline structure).

Fibers having confinement regions such as shown in FIG. 2D can beprepared by depositing one or more annular layers onto a surface of acylinder having a spiral cross-section to form a preform. The photoniccrystal fiber can then be drawn from the preform.

Annular layers can be deposited onto a surface of the spiral cylinderusing a variety of deposition methods. For example, where the spiralportion is between the annular portion and the core, material can beevaporated or sputtered onto the outer surface of the spiral article toform the preform.

In embodiments where the annular portion of the photonic crystal fiberis between the spiral portion and the core, material can be deposited onthe inner surface of the spiral article by, for example, chemical vapordeposition (e.g., plasma enhanced chemical vapor deposition). Methodsfor depositing layers of, for example, one or more glasses onto an innersurface of a cylindrical preform are described in U.S. patentapplication Ser. No. 10/720,453, entitled “DIELECTRIC WAVEGUIDE ANDMETHOD OF MAKING THE SAME,” filed on Nov. 24, 2003, the entire contentsof which are hereby incorporated by reference.

In general, a confinement region may include photonic crystal structuresdifferent from a multilayer configuration. For example, confinementregion 220C includes both a spiral portion and annular portion, in someembodiments, confinement regions can include portions with othernon-spiral structure. For example, a confinement region can include aspiral portion and a holey portion (e.g., composed of a solid cylinderperforated by a number of holes that extend along the fiber's axis). Theholes can be arranged along concentric circles, providing a variation inthe radial refractive index of the holey portion of the confinementregion.

With regard to the composition of confinement region 220, thecomposition of high index and low index layers are typically selected toprovide a desired refractive index contrast between the layers at thefiber's operational wavelength(s). The composition of each high indexlayer can be the same or different as other high index layers, just asthe composition of each low index layer can be the same or different asother low index layers.

Suitable materials for high and low index layers can include inorganicmaterials such as inorganic glasses or amorphous alloys. Examples ofinorganic glasses include oxide glasses (e.g., heavy metal oxideglasses), halide glasses and/or chalcogenide glasses, and organicmaterials, such as polymers. Examples of polymers includeacrylonitrile-butadiene-styrene (ABS), poly methylmethacrylate (PMMA),cellulose acetate butyrate (CAB), polycarbonates (PC), polystyrenes (PS)(including, e.g., copolymers styrene-butadiene (SBC),methylestyrene-acrylonitrile, styrene-xylylene, styrene-ethylene,styrene-propylene, styrene-acylonitrile (SAN)), polyetherimide (PEI),polyvinyl acetate (PVAC), polyvinyl alcohol (PVA), polyvinyl chloride(PVC), polyoxymethylene; polyformaldehyde (polyacetal) (POM), ethylenevinyl acetate copolymer (EVAC), polyamide (PA), polyethyleneterephthalate (PETP), fluoropolymers (including, e.g.,polytetrafluoroethylene (PTFE), polyperfluoroalkoxythylene (PFA),fluorinated ethylene propylene (FEP)), polybutylene terephthalate(PBTP), low density polyethylene (PE), polypropylene (PP), poly methylpentenes (PMP) (and other polyolefins, including cyclic polyolefins),polytetrafluoroethylene (PTFE), polysulfides (including, e.g.,polyphenylene sulfide (PPS)), and polysulfones (including, e.g.,polysulfone (PSU), polyehtersulfone (PES), polyphenylsulphone (PPSU),polyarylalkylsulfone, and polysulfonates). Polymers can be homopolymersor copolymers (e.g., (Co)poly(acrylamide-acrylonitrile) and/oracrylonitrile styrene copolymers). Polymers can include polymer blends,such as blends of polyamides-polyolefins, polyamides-polycarbonates,and/or PES-polyolefins, for example.

Further examples of polymers that can be used include cyclic olefinpolymers (COPs) and cyclic olefin copolymers (COCs). In someembodiments, COPs and COCs can be prepared by polymerizing norbornenmonomers or copolymerization norbornen monomers and other polyolefins(polyethylene, polypropylene). Commercially-available COPs and/or COCscan be used, including, for example, Zeonex® polymers (e.g., Zeonex®E48R) and Zeonor® copolymers (e.g., Zeonor® 1600), both available fromZeon Chemicals L.P. (Louisville, Ky.). COCs can also be obtained fromPromerus LLC (Brecksville, Ohio) (e.g., such as FS1700).

Alternatively, or additionally, low-index regions may be fabricated byusing hollow structural support materials, such as silica spheres orhollow fibers, to separate high-index layers or regions. Examples offibers that include such structural supports are described in PublishedInternational Application WO 03/058308, entitled “BIREFRINGENT OPTICALFIBRES,” the entire contents of which are hereby incorporated byreference.

In certain embodiments, the confinement region is a dielectricconfinement region, being composed of substantially all dielectricmaterials, such as one or more glasses and/or one or more dielectricpolymers. Generally, a dielectric confinement region includessubstantially no metal layers.

In some embodiments, the high index layers or low index layers of theconfinement region can include chalcogenide glasses (e.g., glassescontaining a chalcogen element, such as sulphur, selenium, and/ortellurium). In addition to a chalcogen element, chalcogenide glasses mayinclude one or more of the following elements: boron, aluminum, silicon,phosphorus, sulfur, gallium, germanium, arsenic, indium, tin, antimony,thallium, lead, bismuth, cadmium, lanthanum and the halides (fluorine,chlorine, bromide, iodine).

Chalcogenide glasses can be binary or ternary glasses, e.g., As—S,As—Se, Ge—S, Ge—Se, As—Te, Sb—Se, As—S—Se, S—Se—Te, As—Se—Te, As—S—Te,Ge—S—Te, Ge—Se—Te, Ge—S—Se, As—Ge—Se, As—Ge—Te, As—Se—Pb, As—S—Tl,As—Se—Tl, As—Te—Tl, As—Se—Ga, Ga—La—S, Ge—Sb—Se or complex,multi-component glasses based on these elements such as As—Ga—Ge—S,Pb—Ga—Ge—S, etc. The ratio of each element in a chalcogenide glass canbe varied.

In certain embodiments, in addition or alternative to chalcogenideglass(es), one or more layers in confinement region 220 can include oneor more oxide glasses (e.g., heavy metal oxide glasses), halide glasses,amorphous alloys, or combinations thereof.

In general, the absorption of the high and low index layers variesdepending on their composition and on the fiber's operationalwavelength(s). In some embodiments, the material forming both the highand low index layers can have low absorption. A low absorption materialhas absorption of about 100 dB/m or less at the wavelength of operation(e.g., about 20 dB/m or less, about 10 dB/m or less, about 5 dB/m orless, about 1 dB/m or less, 0.1 dB/m or less). Examples of lowabsorption materials include chalcogenide glasses, which, at wavelengthsof about 3 microns, exhibit an absorption coefficient of about 4 dB/m.At wavelengths of about 10.6 microns, chalcogenide glasses exhibit anabsorption coefficient of about 10 dB/m. As another example, oxideglasses (e.g., lead borosilicate glasses, or silica) can have lowabsorption for wavelengths between about 1 and 2 microns. Some oxideglasses can have an absorption coefficient of about 1 dB/m to 0.0002dB/m in this wavelength range.

Alternatively, one or both of the high and low index materials can havehigh absorption (e.g., about 100 dB/m or more, such as about 1,000 ormore, about 10,000 or more, about 20,000 or more, about 50,000 dB/m ormore). For example, many polymers exhibit an absorption coefficient ofabout 10⁵ dB/m for wavelengths between about 3 and about 11 microns.Examples of such polymers include polyetherimide (PEI),polychlorotrifluoro ethylene (PCTFE), perfluoroalkoxyethylene (PFA), andpolyethylene naphthalate (PEN). PEI has an absorption of more than about10⁵ dB/m at 3 microns, while PCTFE, PFA, and PEN have absorptions ofmore than about 10⁵ dB/m at 10.6 microns.

In some embodiments, the high index material has a low absorptioncoefficient and the low absorption material has a high absorptioncoefficient, or vice versa.

A material's absorption can be determined by measuring the relativetransmission through at least two different thicknesses, T₁ and T₂, ofthe material. Assuming the field in the material decays with thickness Taccording to Pe^(−αT), with P representing the power incident on thematerial, the measured transmitted power through thicknesses T₁ and T₂will then be P₁=Pe^(−αT), and P₂=Pe^(−αT) ² . The absorption coefficientα is then obtained as

$\alpha = {{- \frac{1}{T_{2} - T_{1}}}{{\ln\left( {P_{2}/P_{1}} \right)}.}}$If desired, a more accurate evaluation of α can be obtained by usingseveral thicknesses and performing a least squares fit to the logarithmof the transmitted power.

As discussed previously, materials can be selected for the confinementregion to provide advantageous optical properties (e.g., low absorptionwith appropriate indices of refraction at the guided wavelength(s)).However, the materials should also be compatible with the processes usedto manufacture the fiber. In some embodiments, the high and low indexmaterials should preferably be compatible for co-drawing. Criteria forco-drawing compatibility are provided in aforementioned U.S. patentapplication Ser. No. 10/121,452, entitled “HIGH INDEX-CONTRAST FIBERWAVEGUIDES AND APPLICATIONS.” In addition, the high and low indexmaterials should preferably be sufficiently stable with respect tocrystallization, phase separation, chemical attack and unwantedreactions for the conditions (e.g., environmental conditions such astemperature, humidity, and ambient gas environment) under which thefiber is formed, deployed, and used.

When making a robust fiber waveguides using a drawing process, not everycombination of materials with desired optical properties is necessarilysuitable. Typically, one should select materials that are Theologically,thermo-mechanically, and physico-chemically compatible. Several criteriafor selecting compatible materials will now be discussed.

A first criterion is to select materials that are rheologicallycompatible. In other words, one should select materials that havesimilar viscosities over a broad temperature range, corresponding to thetemperatures experience during the different stages of fiber drawing andoperation. Viscosity is the resistance of a fluid to flow under anapplied shear stress. Here, viscosities are quoted in units of Poise.Before elaborating on rheological compatibility, it is usefule define aset of characteristic temperatures for a given material, which aretemperatures at which the given material has a specific viscosity.

The annealing point, T_(a), is the temperature at which a material has aviscosity 10¹³ Poise. T_(a) can be measured using a Model SP-2A Systemfrom Orton Ceramic Foundation (Westerville, Ohio). Typically, T_(a) isthe temperature at which the viscosity of a piece of glass is low enoughto allow for relief of residual stresses.

The softening point, T_(s), is the temperature at which a material has aviscosity 10^(7.65) Poise. T_(s) can be measured using a softening pointinstrument, e.g., Model SP-3A from Orton Ceramic Foundation(Westerville, Ohio). The softening point is related to the temperatureat which the materials flow changes from plastic to viscous in nature.

The working point, T_(w), is the temperature at which a material has aviscosity 10⁴ Poise. T_(w) can be measured using a glass viscometer,e.g., Model SP-4A from Orton Ceramic Foundation (Westerville, Ohio). Theworking point is related to the temperature at which a glass can beeasily drawn into a fiber. In some embodiments, for example, where thematerial is an inorganic glass, the material's working point temperaturecan be greater than 250° C., such as about 300° C., 400° C., 500° C. ormore.

The melting point, T_(m), is the temperature at which a material has aviscosity 10² Poise. T_(m) can also be measured using a glassviscometer, e.g., Model SP-4A from Orton Ceramic Foundation(Westerville, Ohio). The melting point is related to the temperature atwhich a glass becomes a liquid and control of the fiber drawing processwith respect to geometrical maintenance of the fiber becomes verydifficult.

To be rheologically compatible, two materials should have similarviscosities over a broad temperature range, e.g., from the temperatureat which the fiber is drawn down to the temperature at which the fibercan no longer release stress at a discernible rates (e.g., at T_(a)) orlower. Accordingly, the working temperature of two compatible materialsshould be similar, so that the two materials flow at similar rates whendrawn. For example, if one measures the viscosity of the first material,η₁(T) at the working temperature of the second material, T_(w2),η₁(T_(w2)) should be at least 10³ Poise, e.g., 10⁴ Poise or 10⁵ Poise,and no more than 10⁷ Poise. Moreover, as the drawn fiber cools thebehavior of both materials should change from viscous to elastic atsimilar temperatures. In other words, the softening temperature of thetwo materials should be similar. For example, at the softeningtemperature of the second material, T_(s2), the viscosity of the firstmaterial, η₁(T_(s2)) should be at least 10⁶ Poise, e.g., 10⁷ Poise or10⁸ Poise and no more than 10⁹ Poise. In preferred embodiments, itshould be possible to anneal both materials together, so at theannealing temperature of the second material, T_(a2), the viscosity ofthe first material, η₁(T_(a2)) should be at least 10⁸ Poise (e.g., atleast 10⁹ Poise, at least 10¹⁰ Poise, at least 10¹¹ Poise, at least 10¹²Poise, at least 10¹³ Poise, at least 10¹⁴ Poise).

Additionally, to be rheologically compatible, the change in viscosity asa function of temperature (i.e., the viscosity slope) for both materialsshould preferably match as close as possible.

A second selection criterion is that the thermal expansion coefficients(TEC) of each material should be similar at temperatures between theannealing temperatures and room temperature. In other words, as thefiber cools and its rheology changes from liquid-like to solid-like,both materials' volume should change by similar amounts. If the twomaterials TEC's are not sufficiently matched, a large differentialvolume change between two fiber portions can result in a large amount ofresidual stress buildup, which can cause one or more portions to crackand/or delaminate. Residual stress may also cause delayed fracture evenat stresses well below the material's fracture stress. The TEC is ameasure of the fractional change in sample length with a change intemperature. This parameter can be calculated for a given material fromthe slope of a temperature-length (or equivalently, temperature-volume)curve. The temperature-length curve of a material can be measured usinge.g., a dilatometer, such as a Model 1200D dilatometer from OrtonCeramic Foundation (Westerville, Ohio). The TEC can be measured eitherover a chosen temperature range or as the instantaneous change at agiven temperature. This quantity has the units ° C.⁻¹.

For many materials, there are two linear regions in thetemperature-length curve that have different slopes. There is atransition region where the curve changes from the first to the secondlinear region. This region is associated with a glass transition, wherethe behavior of a glass sample transitions from that normally associatedwith a solid material to that normally associated with a viscous fluid.This is a continuous transition and is characterized by a gradual changein the slope of the temperature-volume curve as opposed to adiscontinuous change in slope. A glass transition temperature, T_(g),can be defined as the temperature at which the extrapolated glass solidand viscous fluid lines intersect. The glass transition temperature is atemperature associated with a change in the materials rheology from abrittle solid to a solid that can flow. Physically, the glass transitiontemperature is related to the thermal energy required to excite variousmolecular translational and rotational modes in the material. The glasstransition temperature is often taken as the approximate annealingpoint, where the viscosity is 10¹³ Poise, but in fact, the measuredT_(g) is a relative value and is dependent upon the measurementtechnique.

A dilatometer can also be used to measure a dilatometric softeningpoint, T_(ds). A dilatometer works by exerting a small compressive loadon a sample and heating the sample. When the sample temperature becomessufficiently high, the material starts to soften and the compressiveload causes a deflection in the sample, when is observed as a decreasein volume or length. This relative value is called the dilatometricsoftening point and usually occurs when the materials viscosity isbetween 10¹⁰ and 10^(12.5) Poise. The exact T_(ds) value for a materialis usually dependent upon the instrument and measurement parameters.When similar instruments and measurement parameters are used, thistemperature provides a useful measure of different materials rheologicalcompatibility in this viscosity regime.

As mentioned above, matching the TEC is an important consideration forobtaining fiber that is free from excessive residual stress, which candevelop in the fiber during the draw process. Typically, when the TEC'sof the two materials are not sufficiently matched, residual stressarises as elastic stress. The elastic stress component stems from thedifference in volume contraction between different materials in thefiber as it cools from the glass transition temperature to roomtemperature (e.g., 25° C.). The volume change is determined by the TECand the change in temperature. For embodiments in which the materials inthe fiber become fused or bonded at any interface during the drawprocess, a difference in their respective TEC's will result in stress atthe interface. One material will be in tension (positive stress) and theother in compression (negative stress), so that the total stress iszero. Moderate compressive stresses themselves are not usually a majorconcern for glass fibers, but tensile stresses are undesirable and maylead to failure over time. Hence, it is desirable to minimize thedifference in TEC's of component materials to minimize elastic stressgeneration in a fiber during drawing. For example, in a composite fiberformed from two different materials, the absolute difference between theTEC's of each glass between T_(g) and room temperature measured with adilatometer with a heating rate of 3° C./min, should be no more thanabout 5×10⁻⁶° C.⁻¹ (e.g., no more than about 4×10⁻⁶° C.⁻¹, no more thanabout 3×10⁻⁶° C.⁻¹, no more than about 2×10⁻⁶° C.⁻¹, no more than about1×10⁻⁶° C.⁻¹, no more than about 5×10⁻⁷° C.⁻¹, no more than about4×10⁻⁷° C.⁻¹, no more than about 3×10⁻⁷° C.⁻¹, no more than about2×10⁻⁷° C.⁻¹).

While selecting materials having similar TEC's can minimize an elasticstress component, residual stress can also develop from viscoelasticstress components. A viscoelastic stress component arises when there issufficient difference between strain point or glass transitiontemperatures of the component materials. As a material cools below T_(g)it undergoes a sizeable volume contraction. As the viscosity changes inthis transition upon cooling, the time needed to relax stress increasesfrom zero (instantaneous) to minutes. For example, consider a compositepreform made of a glass and a polymer having different glass transitionranges (and different T_(g)'s). During initial drawing, the glass andpolymer behave as viscous fluids and stresses due to drawing strain arerelaxed instantly. After leaving the hottest part of the draw furnace,the fiber rapidly loses heat, causing the viscosities of the fibermaterials to increase exponentially, along with the stress relaxationtime. Upon cooling to its T_(g), the glass and polymer cannotpractically release any more stress since the stress relaxation time hasbecome very large compared with the draw rate. So, assuming thecomponent materials possess different T_(g) values, the first materialto cool to its T_(g) can no longer reduce stress, while the secondmaterial is still above its T_(g) and can release stress developedbetween the materials. Once the second material cools to its T_(g),stresses that arise between the materials can no longer be effectivelyrelaxed. Moreover, at this point the volume contraction of the secondglass is much greater than the volume contraction of the first material(which is now below its T_(g) and behaving as a brittle solid). Such asituation can result sufficient stress buildup between the glass andpolymer so that one or both of the portions mechanically fail. Thisleads us to a third selection criterion for choosing fiber materials: itis desirable to minimize the difference in T_(g)'s of componentmaterials to minimize viscoelastic stress generation in a fiber duringdrawing. Preferably, the glass transition temperature of a firstmaterial, T_(g1), should be within 100° C. of the glass transitiontemperature of a second material, T_(g2) (e.g., |T_(g1)−T_(g2)| shouldbe less than 90° C., less than 80° C., less than 70° C., less than 60°C., less than 50° C., less than 40° C., less than 30° C., less than 20°C., less than 10° C.).

Since there are two mechanisms (i.e., elastic and viscoelastic) todevelop permanent stress in drawn fibers due to differences betweenconstituent materials, these mechanisms may be employed to offset oneanother. For example, materials constituting a fiber may naturallyoffset the stress caused by thermal expansion mismatch if mismatch inthe materials T_(g)'s results in stress of the opposite sign.Conversely, a greater difference in T_(g) between materials isacceptable if the materials' thermal expansion will reduce the overallpermanent stress. One way to assess the combined effect of thermalexpansion and glass transition temperature difference is to compare eachcomponent materials' temperature-length curve. After finding T_(g) foreach material using the foregoing slope-tangent method, one of thecurves is displaced along the ordinate axis such that the curvescoincide at the lower T_(g) temperature value. The difference in y-axisintercepts at room temperature yields the strain, ε, expected if theglasses were not conjoined. The expected tensile stress, σ, for thematerial showing the greater amount of contraction over the temperaturerange from T_(g) to room temperature, can be computed simply from thefollowing equation:σ=E·ε,  (4)where E is the elastic modulus for that material. Typically, residualstress values less than about 100 MPa (e.g., about 50 MPa or less, about30 MPa or less), are sufficiently small to indicate that two materialsare compatible.

A fourth selection criterion is to match the thermal stability ofcandidate materials. A measure of the thermal stability is given by thetemperature interval (T_(x)−T_(g)), where T_(x) is the temperature atthe onset of the crystallization as a material cools slowly enough thateach molecule can find its lowest energy state. Accordingly, acrystalline phase is a more energetically favorable state for a materialthan a glassy phase. However, a material's glassy phase typically hasperformance and/or manufacturing advantages over the crystalline phasewhen it comes to fiber waveguide applications. The closer thecrystallization temperature is to the glass transition temperature, themore likely the material is to crystallize during drawing, which can bedetrimental to the fiber (e.g., by introducing optical inhomogeneitiesinto the fiber, which can increase transmission losses). Usually athermal stability interval, (T_(x)−T_(g)) of at least about 80° C.(e.g., at least about 100° C.) is sufficient to permit fiberization of amaterial by drawing fiber from a preform. In preferred embodiments, thethermal stability interval is at least about 120° C., such as about 150°C. or more, such as about 200° C. or more. T_(x) can be measured using athermal analysis instrument, such as a differential thermal analyzer(DTA) or a differential scanning calorimeter (DSC).

A further consideration when selecting materials that can be co-drawnare the materials' melting temperatures, T_(m). At the meltingtemperature, the viscosity of the material becomes too low tosuccessfully maintain precise geometries during the fiber draw process.Accordingly, in preferred embodiments the melting temperature of onematerial is higher than the working temperature of a second,rheologically compatible material. In other words, when heating apreform, the preform reaches a temperature at it can be successfullydrawn before either material in the preform melts.

One example of a pair of materials which can be co-drawn and whichprovide a photonic crystal fiber waveguide with high index contrastbetween layers of the confinement region are As₂Se₃ and the polymer PES.As₂Se₃ has a glass transition temperature (T_(g)) of about 180° C. and athermal expansion coefficient (TEC) of about 24×10⁻⁶/° C. At 10.6 μm,As₂Se₃ has a refractive index of 2.7775, as measured by Hartouni andcoworkers and described in Proc. SPIE, 505, 11 (1984), and an absorptioncoefficient, α, of 5.8 dB/m, as measured by Voigt and Linke anddescribed in “Physics and Applications of Non-Crystalline Semiconductorsin Optoelectronics,” Ed. A. Andriesh and M. Bertolotti, NATO ASI Series,3. High Technology, Vol. 36, p. 155 (1996). Both of these references arehereby incorporated by reference in their entirety. PES has a TEC ofabout 55×10⁻⁶/° C. and has a refractive index of about 1.65.

Embodiments of photonic crystal fibers and methods for forming photoniccrystal fibers are described in the following patents and patentapplications: U.S. Pat. No. 6,625,364, entitled “LOW-LOSS PHOTONICCRYSTAL WAVEGUIDE HAVING LARGE CORE RADIUS;” U.S. Pat. No. 6,563,981,entitled “ELECTROMAGNETIC MODE CONVERSION IN PHOTONIC CRYSTAL MULTIMODEWAVEGUIDES;” U.S. patent application Ser. No. 10/057,440, entitled“PHOTONIC CRYSTAL OPTICAL WAVEGUIDES HAVING TAILORED DISPERSIONPROFILES,” and filed on Jan. 25, 2002; U.S. patent application Ser. No.10/121,452, entitled “HIGH INDEX-CONTRAST FIBER WAVEGUIDES ANDAPPLICATIONS,” and filed on Apr. 12, 2002; U.S. Pat. No. 6,463,200,entitled “OMNIDIRECTIONAL MULTILAYER DEVICE FOR ENHANCED OPTICALWAVEGUIDING;” Provisional 60/428,382, entitled “HIGH POWER WAVEGUIDE,”and filed on Nov. 22, 2002; U.S. patent application Ser. No. 10/196,403,entitled “METHOD OF FORMING REFLECTING DIELECTRIC MIRRORS,” and filed onJul. 16, 2002; U.S. patent application Ser. No. 10/720,606, entitled“DIELECTRIC WAVEGUIDE AND METHOD OF MAKING THE SAME,” and filed on Nov.24, 2003; U.S. patent application Ser. No. 10/733,873, entitled “FIBERWAVEGUIDES AND METHODS OF MAKING SAME,” and filed on Dec. 10, 2003. Thecontents of each of the above mentioned patents and patent applicationsare hereby incorporated by reference in their entirety.

Referring again to FIG. 1, in some embodiments, photonic crystal fiber120 can be can be designed so that the fiber bends preferably in acertain plane. For example, referring to FIG. 3, a photonic crystalfiber 300 includes a cladding 360 that has an asymmetric cross-sectionwith a larger diameter along a major axis 361 compared to its diameteralong a minor axis 362 orthogonal to the major axis. The major and minoraxes are orthogonal to axis 399. The asymmetric cross-section is alsomanifested in the shape of the cladding's outer surface, which includesportions of differing curvature. In particular, cladding 360 includesarcuate portions 331 and 332 and two straight portions 333 and 334.Arcuate portions 331 and 332 are on opposite sides of the cladding alongmajor axis 321. Straight portions 333 and 334 are on opposite sides ofthe cladding along minor axis 322.

In general, the asymmetry of the cross-sectional profile of cladding 360is sufficient to cause fiber 300 to preferably bend in a plane definedby fiber axis 399 and the minor axis 362 during normal use of the fiber.

The ratio of fiber 300's diameter along the major axis to its diameteralong the minor axis can vary. Typically, this ration is selected sothat fiber 300 bends preferably in the bend plane, while cladding 300still provides the desired mechanical support or other function(s) forwhich it is designed (e.g., optical function, thermal management). Insome embodiments, this ratio can be relatively low, such as about 1.5:1or less (e.g., about 1.3:1 or less, about 1.1:1 or less). Alternatively,in certain embodiments, this ratio can be larger than about 1.5:1 (e.g.,about 1.8:1 or more, about 2:1 or more).

Photonic crystal fiber 300 also includes a core 320 and a confinementregion 310 that includes spiral layers 330, 340, and 350, and has aninner seam 321 and an outer seam 322 corresponding to the edges of thecontinuous layers from which the confinement region is formed. Innerseam 321 is located along an azimuth 323 that is displaced by an angle αfrom minor axis 362. α can be about 10° or more (e.g., about 20° ormore, about 30° or more, about 40° or more, about 50° or more, about 60°or more, about 70° or more, about 80° or more). In some embodiments, αis about 90°.

The inner seam does not lie in the preferred bending plane of the fiber.In fiber 300, this is achieved by locating inner seam 321 away from theminor axis. Locating the inner seam away from the preferred bendingplane can be advantageous since it is believed that losses (e.g., due toscattering and/or absorption) of guided radiation is higher at the seamcompared to other portions of the confinement region. Further, it isbelieved that the energy density of guided radiation in the core ishigher towards the outside of a bend in the fiber relative to the energydensity at other parts of the core. By locating the inner seam relativeto the minor axis so that the seam is unlikely to lie in the preferredbending plane (e.g., where α is about 90°), the probability that theinner seam will lie towards the outside of a fiber bend is reduced.Accordingly, the compounding effect of having a relatively high lossportion of the confinement region at the region where the energy densityof guided radiation is high can be avoided, reducing the loss associatedwith bends in the fiber.

Although inner seam 321 and outer seam 322 are positioned at the sameazimuthal position with respect to axis 399 in fiber 300, in otherembodiments the inner and outer seams can be located along at differentrelative azimuthal positions with respect to the fiber's axis.

As discussed previously, the cladding provides mechanical support forthe fiber's confinement region. Accordingly, the thickness of cladding360 can vary as desired along major axis 361. The thickness of cladding360 along minor axis 362 can also vary but is generally less than thethickness along the major axis. In some embodiments, cladding 360 issubstantially thicker along the major axis than confinement region 310.For example, cladding 360 can be about 10 or more times thicker thanconfinement region 310 (e.g., more than about 20, more than about 30,more than about 50 times thicker) along the major axis.

Fiber asymmetry can be introduced by shaving the perform, and thendrawing the fiber from the perform that has an asymmetric cross-section.Alternatively, in some embodiments, the fiber asymmetry can beintroduced after the fiber is drawn from a perform. For example, a fibercan be shaved or ground as part of the production process after beingdrawn but before being spooled.

Although fiber 300 includes a confinement region that has a seam, ingeneral, embodiments of asymmetric fibers can include confinementregions with no seams (e.g., confinement regions that are formed from anumber of annular layers).

Furthermore, while fiber 300 has a shape composed of two circular arcsand two straight lines, in general, fibers can have other shapes. Forexample, fibers can have asymmetric polygonal shapes, can be formed fromarcuate portions having different radii of curvature, and/or fromarcuate portions that curve in opposite directions. Generally, the shapeshould provide the fiber with a preferred bending plane.

While the foregoing fibers are asymmetric with respect to theircross-sectional shape, in general, fibers can be asymmetric in a varietyof ways in order to provide a preferred bend plane. For example, in someembodiments, fibers can include material asymmetries that give rise to apreferred bend plane. Material asymmetries refer to variations betweenthe material properties of different portions of a fiber that cause thefiber to bend preferably in a particular way. For example, a portion ofa fiber cladding can be formed from a material that is mechanically lessrigid that other portions, causing the fiber to bend preferably at thatportion. Mechanical variations can be caused by compositional changes orby physical differences in portions having the same composition.Compositional differences can be introduced, e.g., by doping portions ofa fiber or fiber preform with a dopant that alters the mechanicalproperties of a fiber. As another example, compositional differences canbe introduced by forming different portions of a fiber from differentcompounds. Physical differences refer to, e.g., differences in thedegree of crystallinity in different portions of a fiber. Physicaldifferences, such as differences in crystallinity, can be introduced byselectively heating and/or cooling portions of a fiber during fiberfabrication, and/or using different rates of heating/cooling ondifferent fiber portions.

Furthermore, in some embodiments, fibers can include a symmetric firstcladding, but can include additional structure outside of the claddingthat cause the fiber to bend preferably in a particular plane. Forexample, fibers can be placed in one or more sheaths that are asymmetricwhen it comes to allowing the fiber to bend.

Referring again to FIG. 1, laser system 100 also includes a coolingapparatus 170, which delivers a cooling fluid (e.g., a gas or a liquid)to fiber 120 via a delivery tube 171 and coupling assembly 130. Thecooling fluid is pumped through the core and absorbs heat from the fibersurface adjacent the core. In the present embodiment, the cooling fluidflows in the same direction as the radiation from laser 110, however, insome embodiments, the cooling fluid can be pumped counter to thedirection of propagation of the laser radiation.

The flow rate of the cooling fluid through the core of photonic crystalfiber 120 can vary as desired. Typically, the flow rate depends on theoperating power of the laser, the absorption of the fiber at theoperating wavelength, the length of the fiber, and the size of the fibercore, for example. Generally, the flow rate should be sufficient to coolthe fiber at its operating power. In some embodiments, the flow rate canbe about 0.1 liters/min or more (e.g., about 0.5 liters/min or more,about 1 liter/min or more, about 2 liters/min or more, about 5liters/min or more, about 8 liters/min or more, about 9 liters/min ormore, about 10 liters/min or more).

The pressure of cooling fluid exhausted from the fiber can vary. In someembodiments, the pressure of the cooling fluid can be relatively high.For example, where the fluid exits from the same end of the fiber as theradiation, a cooling gas can be at sufficiently high pressure to cleardebris from the target tissue of the patient. The gas pressure can beabout 0.2 PSI or more (e.g., about 0.5 PSI or more, about 1 PSI ormore). In some embodiments, the pressure of a gas exiting the core of afiber can correspond to a flow rate of about 1 liter/min or more (e.g.,about 2 liter/min or more, about 5 liter/min or more, about 8 liter/minor more, about 10 liter/min or more) through a 1 meter length of fiberhaving a core diameter of about 500 μm.

The flow rate can be nominally constant while the system is activated,or can vary depending on the state operation of the laser system. Forexample, in some embodiments, the flow rate can be adjusted based onwhether radiation is being directed through fiber 120 or not. At timeswhere the laser is activated and radiation is directed through thefiber, the flow rate can be at a level sufficient to adequately cool thefiber. However, between radiation doses, the system can reduce the flowrate to a lower level (e.g., about 10% or less than the rate used tocool the fiber while the laser is activated). The gas flow rate can betriggered using remote control 152 or an additional remote control thatthe operator can easily operate while using the system.

In general, the temperature of the cooling fluid directed to the fibercan vary. In some embodiments, the cooling fluid is directed to thefiber at ambient temperature (e.g., at room temperature). In certainembodiments, the cooling fluid is cooled below ambient temperature priorto cooling the fiber. The cooling fluid can be cooled so that fluidexhausted from the fiber is within a certain temperature range. Forexample, the cooling fluid can be sufficiently cooled so that fluidexhausted from the fiber does not scald the patient if it comes intocontact with the patient. As another example, the cooling fluid can besufficiently cooled so that fluid exhausted from the fiber is betweenroom temperature and body temperature. In some embodiments, the coolingfluid directed to the fiber can be cooled so that it has a temperaturebelow room temperature. For example, the fluid can have a temperature ofabout 20° C. or less (e.g., about 10° C. or less, about 0° C. or less,about −10° C. or less, about −20° C. or less, about −50° C. or less).

In certain embodiments, where the cooling fluid flows through the fibercore in the laser radiation propagation direction, it can performadditional functions where it impinges on the target tissue of thepatient. For example, in some embodiments, heated fluid (e.g., gas)exiting the fiber can reduce bleeding at incised blood vessels (or othertissue) by enhancing coagulation of the blood. It is believed thatcoagulation of blood is accelerated at temperatures of about 60° C. ormore. Accordingly, where the gas exiting the fiber impinging the targettissue is about 60° C. or more, it can increase the rate at which bloodcoagulates, which can assist the surgeon by reducing the need to suctionblood from the operating area. In some embodiments, the temperature ofgas exiting the fiber can be, for example, about 50° C. or more, about60° C. or more, about 65° C. or more, about 70° C. or more, about 80° C.or more, about 90° C. or more, about 100° C. or more). Alternatively, incertain embodiments, the temperature of the gas exiting the fiber can bebelow room temperature (e.g., about 10° C. or less, about 0° C. orless). For example, the system can provide cooled gas to the targetlocation in procedures where it is beneficial to cool tissue beforeirradiating the tissue. In certain embodiments, the temperature of gasexiting the fiber can be approximately at body temperature (e.g., atabout 37° C.),

Gas flowing through the fiber core can be heated by about 5-10° C./Wattof input power (e.g., about 7-8° C./Watt). For example, a fiber havingan input power of about 20 Watts could heat gas flowing through its coreby about 100-200° C.

In some embodiments, the fluid flowing through the fiber's core can beused to deliver other substances to the target tissue. For example,atomized pharmaceutical compounds could be introduced into a gas that isflowed through the core and delivered via the photonic crystal fiber tothe target tissue.

In general, the type of cooling fluid can vary as desired. The coolingfluid can be liquid, gas, or superfluid. In some embodiments, thecooling fluid includes a noble gas (e.g., helium, neon, argon, krypton,and/or xenon), oxygen, carbon dioxide, and/or nitrogen. The coolingfluid can be composed substantially of a single compound (e.g., having apurity of about 98% or more, about 99% or more, about 99.5% or more,about 99.8% or more, about 99.9% or more), or can be a mixture (e.g.,air or heliox).

In some embodiments, the cooling fluid is selected based on its abilityto cool the fiber. The cooling ability of a fluid can depend on thefluids flow rate and/or the fluids thermal conductivity. Helium gas, forexample, has a relatively high thermal conductivity compared to othergases. Furthermore, for a given pressure drop, helium can have a higherflow rate than other gases, such as nitrogen. Accordingly, in someembodiments, helium can be selected based on its ability to cool thefiber better than other gases.

Alternatively, or additionally, the cooling fluid can be selected basedon whether or not it has any adverse interactions with the patient. Forexample, in embodiments where the cooling fluid is in close proximity tothe patient, it can be selected based on its relatively low toxicity. Incertain embodiments, a cooling fluid can be selected based on itssolubility compared to other fluids. A fluid with relatively lowsolubility in blood can reduce the risk of the patient having anembolism due to exposure to the cooling fluid. An example of a fluidwith relatively low toxicity and relatively low solubility is heliumgas.

The cooling fluid can also be selected based on other criteria, such asits reactivity with other elements (e.g., flammability). In someembodiments, a cooling fluid, such as helium, can be selected based onits inert characteristics (e.g., inflammability).

In certain embodiments, a protective sleeve can be attached to theoutput end of photonic crystal fiber 120. Sleeves can be used to preventdebris buildup and clogging of the fiber's output end. An example of asleeve 401 is shown in FIG. 4A. Sleeve 401 is attached to the output endof a photonic crystal fiber 410. Sleeve 401 includes a collar 425 thatmaintains a stand off distance 405 between the output end of the fiberand a distal opening 430 of the sleeve. Typically, stand off distance405 is from about 0.5 cm to about 4 cm long. Radiation 411 exiting core420 of fiber 410 exits the sleeve through distal opening 430.

Sleeve 401 can also include perforations to reduce the pressure of fluidexiting the fiber at distal opening 430. For example, sleeve 401includes secondary openings 435 and 436 that, along with distal opening430, provide paths through which fluid exiting core 420 can exit thesleeve.

Typically, sleeves are formed from rigid materials that can be readilysterilized. For example, sleeves can be formed from stainless steel.Sleeves can be disposable or reusable.

Another example of a sleeve is sleeve 401A shown in FIG. 4B. Sleeve 401Anarrows along its length, having a larger diameter 402B where itattaches to the output end of fiber 401 compared to the diameter 402Anear the distal opening. The narrowing sleeve increases the pressure offluid from core 420 in the sleeve, increasing the fluid pressure atopenings 435A and 435B, thereby reducing the possibility of debris beingsucked into the sleeve through these openings.

In some embodiments, sleeves can include one or more optical components.For example, referring to FIG. 4C, a sleeve 401B can include a reflector440 (e.g., a mirror) attached near the distal opening. Reflector 440redirects radiation 411 exiting core 420, and can enable an operator todirect the radiation into confined spaces not otherwise accessible.

In embodiments, sleeves can also include transmissive opticalcomponents. For example, referring to FIG. 4D, a sleeve 401C includes alens 450 mounted near distal opening 430. Lens is mounted within thesleeve by a lens mount 451, which is positioned between distal opening430 and secondary openings 435 and 436 so that fluid from the fiber canstill exit sleeve 401C through openings 435 and 436. Lens 450 focusesradiation 411 exiting core 420 to a waist at some position beyond distalopening 430. Another example of a transmissive optical component thatcan be mounted within a sleeve is a transmissive optical flats, whichcan serve as a window for the transmission of radiation exiting thefiber core while preventing fluid flow through distal opening 430.

As discussed previously, in laser system 100, light is coupled fromlaser 110 and fluid from fluid source 170 into fiber 120 by couplingassembly 130. Referring to FIG. 5A, an example of a coupler for couplinggas and radiation into a photonic crystal fiber is coupling assembly500. Coupling assembly 500 includes a first portion 510 that receivesradiation from the laser and gas from a gas source, and a second portion520 that connects to photonic crystal fiber 120. First portion 510 iscoupled to second portion 520 by a flexible junction 505 (e.g., ametallic bellows or rubber tube).

First portion 510 includes a lens holder 502 and an adaptor 504 for thelens holder. The lens holder can be a commercially available lensholder. When coupled to lens holder 5-2, adaptor 504 secures a lens 501in the lens holder. An o-ring 503 creates a seal between adaptor 504 andlens 501. Adaptor 504 also includes a fitting 504 a for connecting totube that supplies gas to the system. In some embodiments, fitting 504 aincludes a barbed hose fitting.

Portion 520 includes a connector alignment stage 508 including a fiberoptic connector receptacle (e.g., a commercially available stage, suchas component LP-1A, available from Newport (Irvine, Calif.)). Stage 508is connected to flexible junction 505 by an adaptor 506. An o-ring 507creates a seal between stage 508 and adaptor 506. A fiber opticconnector 509 couples photonic crystal fiber 510 to stage 58. Anothero-ring 511 creates a seal between fiber optic connector 509 and stage508.

Another example of a coupling assembly is shown in FIG. 5B. Couplingassembly 530 includes a laser connector 540 that attaches to the outputterminal 111 of laser 110. Coupling assembly 530 includes a housing 531attached to laser connector 540. The housing includes a fluid inlet port533 and a radiation output port 534. A fiber optic connector 550 affixesto radiation output port 534, positioning an end of a photonic crystalfiber 551 relative to the radiation output port. In addition, aconnector 560 connects a fluid conduit 561 to the housing by attachingto fluid input port 533.

A retardation reflector 532 is positioned within housing 531.Retardation reflector 532 directs linearly polarized radiation 541entering the housing from the laser towards a radiation output terminal534, modifying the polarization state so that reflected radiation 542 iscircularly polarized. More generally, the reflective retarder modifiesthe polarization state of the laser radiation to provide a lower losspolarization to fiber 551. In embodiments, average losses of circularlypolarized radiation may be lower than linearly polarized radiation wherethe fiber has high loss regions that may be coincident with the plane ofpolarization. For example, photonic crystal fibers that have aconfinement region having a seam can exhibit higher losses for radiationpolarized in the plane of the seam compared to circularly polarizedlight. Alternatively, or additionally to having a retarder, fiber 551can be attached with its seam (or other high loss region) in aparticular orientation with respect to the polarization state ofradiation from the laser.

Examples of a reflective retarder suitable for 10.6 micron radiation areseries PRR: Silicon & Copper Phase Retardation Reflectors(commercially-available from Laser Research Optics (Providence, R.I.).Transmissive retarders (e.g., formed from birefringent crystals) can beused in place of, or in addition to, retardation reflector 532.

Coupling assembly 530 also includes a lens 545, mounted within housing531 by mount 535, which focuses reflected radiation 542 to a waist atradiation output port 534 where it couples into the core of fiber 551.Lenses suitable for use at 10.6 micron wavelengths, for example, can beformed from ZnSe.

In embodiments where cooling fluid is not coupled into the fiber's core,other coupling assemblies can be used. Generally, in such embodiments,any coupler suitable for the wavelength and intensity at which the lasersystem operates can be used. One type of a coupler is described by R.Nubling and J. Harrington in “Hollow-waveguide delivery systems forhigh-power, industrial CO₂ lasers,” Applied Optics, 34, No. 3, pp.372-380 (1996). Other examples of couplers include one or more focusingelements, such as one or more lenses. More generally, the coupler caninclude additional optical components, such as beam shaping optics, beamfilters and the like.

In general, coupling efficiency can be relatively high. For example,coupling assembly 130 can couple more than about 70% of the laser outputat the guided wavelength into a guided mode in the fiber (e.g., about80% or more, 90% or more, 95% or more, 98% or more). Coupling efficiencyrefers to the ratio of power guided away by the desired mode to thetotal power incident on the fiber.

While laser system 100 includes handpiece 140, systems can includedifferent types of handpieces depending on the medical application forwhich they are being used. In general, a handpiece includes a portionthat the operator can grip, e.g., in his/her palm or fingertips, and caninclude other components as well. In certain embodiments, handpieces caninclude endoscopes (e.g., flexible or rigid endoscopes), such as acystoscopes (for investigating a patient's bladder), nephroscopes (forinvestigating a patient's kidney), bronchoscopes (for investigating apatient's bronchi), laryngoscopes (for investigating a patient'slarynx), otoscopes (for investigating a patient's ear), arthroscopes(for investigating a patient's joint), laparoscopes (for investigating apatient's abdomen), and gastrointestinal endoscopes. Another example ofa handpiece is a catheter, which allows an operator to position theoutput end of the photonic crystal fiber into canals, vessels,passageways, and/or body cavities.

Moreover, handpieces can be used in conjunction with other components,without the other component being integrated into the handpiece. Forexample, handpieces can be used in conjunction with a trocar to positionthe output end of a photonic crystal fiber within an abdominal cavity ofa patient. In another example, a handpiece can be used in conjunctionwith a rigid endoscope, where the rigid endoscope is not attached to thegripping portion of the handpiece or to the photonic crystal fiber.

Referring to FIG. 6, in some embodiments, a handpiece 680 includes anarrow conduit 684 that includes a channel through which photoniccrystal fiber 120 is inserted. Conduit 684 can be made from a rigid, butdeformable, material (e.g., stainless steel). This allows the operatorto bend the conduit (e.g., by hand or using a tool) to a desired amount(e.g., such as at bend 686) for a procedure, where the conduit retainsthe bend until the operator straightens it or bends it in a differentway. Handpiece 680 also includes a gripping portion 682 attached toconduit 684, which allows the operator to comfortably hold thehandpiece.

In certain embodiments, handpieces can include actuators that allow theoperator to bend the fiber remotely, e.g., during operation of thesystem. For example, referring to FIG. 7A, in some embodiments, laserradiation 112 can be delivered to target tissue 699 within a patient 601using an endoscope 610. Endoscope 610 includes a gripping portion 611and a flexible conduit 615 connected to each other by an endoscope body616. An imaging cable 622 housing a bundle of optical fibers is threadedthrough a channel in gripping portion 611 and flexible conduit 615.Imaging cable 622 provide illumination to target tissue 699 via flexibleconduit 615. The imaging cable also guides light reflected from thetarget tissue to a controller 620, where it is imaged and displayedproviding visual information to the operator. Alternatively, oradditionally, the endoscope can include an eyepiece lens that allows theoperator to view the target area directly through the imaging cable.

Endoscope 610 also includes an actuator 640 that allows the operator tobend or straighten flexible conduit 615. In some embodiments, actuator640 allows flexible conduit 615 to bend in one plane only.Alternatively, in certain embodiments, the actuator allow the flexibleconduit to bend in more than one plane.

Endoscope 610 further includes an auxiliary conduit 630 (e.g., adetachable conduit) that includes a channel through which fiber 120 isthreaded. The channel connects to a second channel in flexible conduit615, allowing fiber 120 to be threaded through the auxiliary conduitinto flexible conduit 615. Fiber 120 is attached to auxiliary conduit ina matter than maintains the orientation of the fiber with respect thechannel through flexible conduit 615, thereby minimizing twisting of thephotonic crystal fiber about its waveguide axis within the flexibleconduit. In embodiments where photonic crystal fiber 120 has aconfinement region that includes a seam, the fiber can be attached tothe auxiliary conduit so that the seam is not coincident with a bendplane of the flexible conduit.

In general, photonic crystal fibers can be used in conjunction withcommercially-available endoscopes, such as endoscopes available fromPENTAX Medical Company (Montvale, N.J.) and Olympus Surgical &Industrial America, Inc. (Orangeburg, N.Y.).

Auxiliary conduit 630 can be configured to allow the user to extendand/or retract the output end of the photonic crystal fiber withinflexible conduit 615. For example, referring to FIG. 7B, in someembodiments, auxiliary conduit 630 of endoscope 610 can include twoportions 631 and 632 that are moveable with respect to each other.Portion 632 is attached to endoscope body 616, while portion 631telescopes with respect to portion 632. Portion 632 includes a connector636 that connects to a fiber connector 638 attached to fiber 120. Themating mechanism of connector 636 and fiber connector 638 can allow forquick and simple removal and attachment of the photonic crystal fiber tothe endoscope. When attached, connector 636 and fiber connector 638substantially prevent fiber 120 from twisting, maintaining itsorientation about the fiber axis within flexible conduit 615. Theconnectors can maintain the orientation of the fiber in the conduit witha seam in the fiber oriented away from a bend plane of the conduit, forexample. Furthermore, when portion 631 extends or retracts with respectto portion 632, it extends or retracts the output end 645 of fiber 120with respect to the distal end 618 of flexible conduit 615. Auxiliaryconduit 630 also includes a locking mechanism 634 (e.g., a latch orclamp) that allows the user to lock the portion 631 with respect toportion 632. The locking mechanism prevents unwanted movement of fiber120 within flexible conduit 615 while radiation is being delivered tothe patient.

While laser systems 100 and 600 include a single length of a photoniccrystal fiber that delivers radiation from laser 110 to the targetlocation, multiple connected lengths of photonic crystal fiber can alsobe used. For example, referring to FIG. 7C, a laser system 700 includestwo lengths of photonic crystal fiber 720 and 721 rather than a singlelength of photonic crystal fiber as laser systems 100 and 600. Photoniccrystal fiber lengths 720 and 721 are coupled together by a connector730 that attaches to auxiliary conduit 630 of endoscope 610.

Laser system 700 includes a secondary cooling apparatus 740 in addition,or alternatively, to cooling apparatus 170. Photonic crystal fiberlength 720 is placed within a sheath 744, which is connected tosecondary cooling apparatus 740 by a delivery tube 742. Secondarycooling apparatus 740 cools photonic crystal fiber length 720 by pumpinga cooling fluid through sheath 744.

Secondary cooling apparatus 740 can recirculate the cooling fluid itpumps through sheath 744. For example, sheath 744 can include anadditional conduit that returns the cooling fluid to secondary coolingapparatus 740. A heat exchanger provided with the secondary coolingsystem can actively cool the exhausted cooling fluid before thesecondary cooling system pumps the fluid back to sheath 744.

The cooling fluid can be the same or different as the cooling fluidpumped into the core of the photonic crystal fiber by cooling apparatus170. In some embodiments, cooling apparatus 170 pumps a gas through thecore of the fiber, while secondary cooling apparatus 740 cools the fiberusing a liquid (e.g., water).

Sheath 744 can perform a protective function, shielding photonic crystalfiber length 720 from environmental hazards. In some embodiments, sheath744 includes a relatively rigid material (e.g., so that sheath 744 ismore rigid than photonic crystal fiber length 720), reducing flexing ofphotonic crystal fiber length 720. In some embodiments, sheath 744 isformed from a relatively rigid material, such as nitinol(commercially-available from Memry, Inc., Bethel, Conn.).

In embodiments, using two lengths of photonic crystal fiber can prolongthe usable lifetime of at least one of the lengths. For example, due tothe additional cooling and/or protection afforded the fiber length bycooling apparatus 740 and/or sheath 744, photonic crystal fiber length720 can be replaced less often than fiber length 721. In someembodiments, fiber length 721 can be used multiple times, while fiberlength 721 is discarded after each use.

While laser system 700 utilizes two connected lengths of photoniccrystal fiber, more generally, waveguides other than photonic crystalwaveguides can also be connected to a length of photonic crystal fiberto provide a conduit for delivering radiation from a laser to the targetlocation. For example, a length of a hollow metallic waveguide can beconnected to a length of a photonic crystal fiber to provide a conduitfor IR radiation.

Furthermore, in general, other conduits can be bundled with photoniccrystal fibers in a medical laser system to, e.g., deliver something to,remove something from, or to observe the target tissue during theprocedure. For example, as discussed in reference to FIG. 7A, thephotonic crystal fiber can be bundled with other optical waveguides,such as an imaging cable used to illuminate and/or image the targettissue using an imaging system. In certain embodiments, laser systemscan deliver radiation from more than one radiation source to the patientby delivering radiation from a laser radiation through the photoniccrystal fiber, and radiation from a second source (e.g., a second laser)through the other conduit (e.g., an optical fiber). As an example,referring to FIG. 8, in certain embodiments, a system 800 includes afiber waveguide 830 and a photonic crystal fiber 810, with a portion offiber waveguide 830 and photonic crystal fiber 810 being bundled withina jacket 850 (e.g., a flexible jacket, such as a flexible polymerjacket). Photonic crystal fiber 810 is coupled to a laser 820, whichdelivers radiation at wavelength λ₁ through the core 812 of photoniccrystal fiber 810. Fiber waveguide 830 is coupled to another radiationsource 840, which delivers radiation at a different wavelength, λ₂,through the core 832 of fiber waveguide 830. Photonic crystal fiber 810and fiber waveguide 830 deliver radiation (indicated by referencenumerals 822 and 842, respectively) at wavelengths λ₁ and λ₂,respectively, to a common location.

Fiber waveguide 830 can be, for example, an optical fiber or a photoniccrystal fiber. Radiation source 840 can be a laser or other light source(e.g., a bulb or light emitting diode). As an example, in someembodiments, radiation source 840 is a laser that emits visibleradiation (e.g., λ₂ is within a range from about 400 nm to about 800 nm,such as 633 nm), such as a HeNe laser and fiber waveguide 830 is anoptical fiber. The visible radiation emitted from fiber 830 allows theoperator to aim the output end of the photonic crystal fiber to theappropriate tissue before delivering laser radiation from laser 820. Inanother example, the other radiation source 840 is an Nd:YAG laser,which can also be used to deliver radiation to the patient forphotocoagulation or photoablation purposes.

Jacket 850 can have a sufficiently small outer diameter to allow thejacket to be used in conjunction with a variety of handpieces. Forexample, the jacket can have an outer diameter of about 2 mm or less,allowing the jacket to be inserted into a standard-size channel of anendoscope.

In some embodiments, the photonic crystal fiber can be bundled with atube for delivering gas to (e.g., hot gas for blood coagulation) orvacuuming debris at the target location, as an alternative or inaddition to being bundled with a fiber waveguide.

For example, referring to FIG. 9, a system 900 a photonic crystal fiber910 is bundled with a tube 930 for exhausting fluid (e.g., coolingfluid) exiting the photonic crystal fiber's core 912 at the fiber'soutput end. The system shown in FIG. 9 includes a laser 920 and a fluidsource 926 that deliver radiation and fluid to the photonic crystalfiber's core 912 via a coupling assembly 924. The system also includes apump that draws fluid exiting core 912 through tube 930 away from thepatient.

The output end of fiber 910 and input end of tube 930 are coupledtogether by a cap 960, that fits over the ends of the fiber and tube.Cap 960 includes a window 962 that is made from a material substantiallytransparent to the wavelength of radiation being delivered from laser920. Cap 960 positions window 962 in the path of radiation 922 exitingcore 912, allowing the system to deliver the radiation to the patient.Fluid exiting core 912, however, is drawn through an exhaust port 964into tube 942. Pump 940, connected to the opposite end of tube 930,draws the fluid 942 through the tube away from the patient.

A portion of tube 930 and photonic crystal fiber 910 are bundledtogether within a jacket 950, providing a flexible duct that can bethreaded through a channel in a handpiece (e.g., a handpiece includingan endoscope).

System 900 can be used in procedures where it is undesirable to exhaustfluid (e.g., cooling fluid) to the tissue being exposed to radiation.For example, where the radiation is being delivered internally, wherethe exhausted fluid is toxic, or is at an undesirable temperature (e.g.,sufficiently hot to burn the exposed tissue), an exhaust tube can beincluded with the photonic crystal fiber to prevent exposure of thetissue to the fluid.

In some cases, the handpiece in a medical laser system can be replacedby a robot, which can be operated remotely. For example, robot-performedsurgery is under consideration in applications where a surgeon cannoteasily or rapidly reach a patient (e.g., a wounded soldier on abattlefield).

Since photonic crystal fibers are used in medical procedures, theyshould be sterilizable. For example, photonic crystal fibers should beable to withstand sterilizing procedures, such as autoclaving.Typically, lengths of photonic crystal fiber are provided to the userpre-sterilized and sealed in a container (e.g., vacuum sealed in acontainer that has sufficient barrier properties to preventcontamination of the fiber length during storage and shipping). Forexample, sterilized lengths of photonic crystal fiber (e.g., about 0.5meters to about 2.5 meters lengths) can be provided sealed (e.g., vacuumsealed) in a plastic container (e.g., including a barrier film layer).

In general, the laser systems described above can be used in a number ofdifferent medical applications. Generally, the type of laser,wavelength, fiber length, fiber outer diameter, and fiber innerdiameter, among other system parameters, will be selected according tothe application. Medical applications include aesthetic medicalprocedures, surgical medical procedures, ophthalmic procedures,veterinary procedures, and dental procedures.

Aesthetic procedures include treatment for: hair removal; pulsed lightskin treatments for reducing fine wrinkle lines, sun damage, age spots,freckles, some birthmarks, rosacea, irregular pigmentation, brokencapillaries, benign brown pigment and pigmentation; skin resurfacing;leg veins; vascular lesions; pigmented lesions; acne; psoriasis &vitiligo; and/or cosmetic repigmentation.

Surgical procedures include procedures for gynecology, laparoscopy,condylomas and lesions of the external genitalia, and/or leukoplakia.Surgical applications can also include ear/nose/throat (ENT) procedures,such as laser assisted uvula palatoplasty (LAUP) (i.e., to stopsnoring); procedures to remove nasal obstruction; stapedotomy;tracheobronchial endoscopy; tonsil ablation; and/or removal of benignlaryngeal lesions. Surgical applications can also include breast biopsy,cytoreduction for metastatic disease, treatment of decubitus or statisulcers, hemorrhoidectomy, laparoscopic surgery, mastectomy, and/orreduction mammoplasty. Surgical procedures can also include proceduresin the field of podiatry, such as treatment of neuromas, periungual,subungual and plantar warts, porokeratoma ablation, and/or radical nailexcision. Other fields of surgery in which lasers may be used includeorthopedics, urology, gastroenterology, and thoracic & pulmonarysurgery.

Ophthalmic uses include treatment of glaucoma, age-related maculardegeneration (AMD), proliferative diabetic retinopathy, retinopathy ofprematurity, retinal tear and detachment, retinal vein occlusion, and/orrefractive surgery treatment to reduce or eliminate refractive errors.

Veterinary uses include both small animal and large animal procedures.

Examples of dental applications include hard tissue, soft tissue, andendodontic procedures. Hard tissue dental procedures include cariesremoval & cavity preparation and laser etching. Soft tissue dentalprocedures include incision, excision & vaporization, treatment of gummysmile, coagulation (hemostasis), exposure of unerupted teeth, aphthousulcers, gingivoplasty, gingivectomy, gingival troughing for crownimpressions, implant exposure, frenectomy, flap surgery, fibromaremoval, operculectomy, incision & drainage of abscesses, oralpapilectomy, reduction of gingival hypertrophy, pre-prosthetic surgery,pericoronitis, peri implantitis, oral lesions, and sulcular debridement.Endodontic procedures include pulpotomy, root canal debridement, andcleaning. Dental procedures also include tooth whitening.

Generally, the type of laser, wavelength, fiber length, fiber outerdiameter, and fiber inner diameter, among other system parameters, areselected according to the application. For example, embodiments in whichthe laser is a CO₂ laser, the laser system can be used for surgicalprocedures requiring the ablation, vaporization, excision, incision, andcoagulation of soft tissue. CO₂ laser systems can be used for surgicalapplications in a variety of medical specialties including aestheticspecialties (e.g., dermatology and/or plastic surgery), podiatry,otolaryngology (e.g., ENT), gynecology (including laparoscopy),neurosurgery, orthopedics (e.g., soft tissue orthopedics), arthroscopy(e.g., knee arthroscopy), general and thoracic surgery (including opensurgery and endoscopic surgery), dental and oral surgery, ophthalmology,genitourinary surgery, and veterinary surgery.

In some embodiments, CO₂ laser systems can be used in the ablation,vaporization, excision, incision, and/or coagulation of tissue (e.g.,soft tissue) in dermatology and/or plastic surgery in the performance oflaser skin resurfacing, laser derm-abrasion, and/or laser burndebridement. Laser skin resurfacing (e.g,. by ablation and/orvaporization) can be performed, for example, in the treatment ofwrinkles, rhytids, and/or furrows (including fine lines and textureirregularities). Laser skin resurfacing can be performed for thereduction, removal, and/or treatment of: keratoses (including actinickeratosis), seborrhoecae vulgares, seborrheic wart, and/or verrucaseborrheica; vermillionectomy of the lip; cutaneous horns; solar/actinicelastosis; cheilitis (including actinic cheilitis); lentigines(including lentigo maligna or Hutchinson's malignant freckle); unevenpigmentation/dyschromia; acne scars; surgical scars; keloids (includingacne keloidalis nuchae); hemangiomas (including Buccal, port wine and/orpyogenic granulomas/granuloma pyogenicum/granuloma telagiectaticum);tattoos; telangiectasia; removal of skin tumors (including periungualand/or subungual fibromas); superficial pigmented lesions;adenosebaceous hypertrophy and/or sebaceous hyperplasia; rhinophymareduction; cutaneous papilloma; milia; debridement of eczematous and/orinfected skin; basal and squamous cel carcinoma (includingkeratoacanthomas, Bowen's disease, and/or Bowenoid Papulosis lesions);nevi (including spider, epidermal, and/or protruding); neurofibromas;laser de-epithelialization; tricoepitheliomas; xanthelasma palpebrarum;and/or syringoma. CO₂ laser systems can be used for laser ablation,vaporization and/or excision for complete and/or partial nailmatrixectomy, for vaporization and/or coagulation of skin lesions (e.g.,benign and/or malignant, vascular and/or avascular), and/or for Moh'ssurgery, for lipectomy. Further examples include using laser system 1300for laser incision and/or excision of soft tissue for the performance ofupper and/or lower eyelid blepharoplasty, and/or for the creation ofrecipient sites for hair transplantation.

In certain embodiments, CO₂ laser systems is used in the laser ablation,vaporization, and/or excision of soft tissue during podiatry proceduresfor the reduction, removal, and/or treatment of: verrucaevulgares/plantar warts (including paronychial, periungual, and subungualwarts); porokeratoma ablation; ingrown nail treatment; neuromas/fibromas(including Morton's neuroma); debridement of ulcers; and/or other softtissue lesions. CO₂ laser systems can also be used for the laserablation, vaporization, and/or excision in podiatry for complete and/orpartial matrixectomy.

CO₂ laser systems can be used for laser incision, excision, ablation,and/or vaporization of soft tissue in otolaryngology for treatment of:choanal atresia; leukoplakia (including oral, larynx, uvula, palatal,upper lateral pharyngeal tissue); nasal obstruction; adult and/orjuvenile papillomatosis polyps; polypectomy of nose and/or nasalpassages; lymphangioma removal; removal of vocal cord/fold nodules,polyps and cysts; removal of recurrent papillomas in the oral cavity,nasal cavity, larynx, pharynx and trachea (including the uvula, palatal,upper lateral pharyngeal tissue, tongue and vocal cords); laser/tumorsurgery in the larynx, pharynx, nasal, ear and oral structures andtissue; Zenker' diverticulum/pharynoesophageal diverticulum (e.g.,endoscopic laser-assisted esophagodiverticulostomy); stenosis (includingsubglottic stenosis); tonsillectomy (including tonsillar cryptolysis,neoplasma) and tonsil ablation/tonsillotomy; pulmonary bronchial andtracheal lesion removal; benign and malignant nodules, tumors andfibromas (e.g., of the larynx, pharynx, trachea,tracheobronchial/endobronchial); benign and/or malignant lesions and/orfibromas (e.g., of the nose or nasal passages); benign and/or malignanttumors and/or fibromas (e.g., oral); stapedotomy/stapedectomy; acousticneuroma in the ear; superficial lesions of the ear (includingchondrodermatitis nondularis chronica helices/Winkler's disease);telangiectasia/hemangioma of larynx, pharynx, and/or trachea (includinguvula, palatal, and/or upper lateral pharyngeal tissue); cordectomy,cordotomy (e.g., for the treatment of vocal cord paralysis/vocal foldmotion impairment), and/or cordal lesions of larynx, pharynx, and/ortrachea; myringotomy/tympanostomy (e.g., tympanic membranefenestration); uvulopalatoplasty (e.g., LAUP); turbinectomy and/orturbinate reduction/ablation; septal spur ablation/reduction and/orseptoplasty; partial glossectomy; tumor resection on oral, subfacialand/or neck tissues; rhinophyma; verrucae vulgares; and/orgingivoplasty/gingivectomy.

In some embodiments, CO₂ laser systems can be used for the laserincision, excision, ablation, and/or vaporization of soft tissue ingynecology for treatment of: conizaton of the cervix (including cervicalintraepithelial neoplasia, vulvar and/or vaginal intraepithelialneoplasia); condyloma acuminata (including cervical, genital, vulvar,preineal, and/or Bowen's disease, and/or Bowenoid papulosa lesions);leukoplakia (e.g., vulvar dystrophies); incision and drainage ofBartholin's and/or nubuthian cysts; herpes vaporization; urethralcaruncle vaporization; cervical dysplasia; benign and/or malignanttumors; and/or hemangiomas.

CO₂ laser systems can be used for the vaporization, incision, excision,ablation and/or coagulation of soft tissue in endoscopic and/orlaparoscopic surgery, including gynecology laparoscopy, for treatmentof: endometrial lesions (inclusing ablation of endometriosis);excision/lysis of adhesions; salpingostomy; oophorectomy/ovariectomy;fimbroplasty; metroplasty; tubal microsurgery; uterine myomas and/orfibroids; ovarian fibromas and/or follicle cysts; uterosacral ligamentablation; and/or hysterectomy.

In certain embodiments, CO₂ laser systems are used for the laserincision, excision, ablation, and/or vaporization of soft tissue inneurosurgery for the treatment of cranial conditions, including:posterior fossa tumors; peripheral neurectomy; benign and/or malignanttumors and/or cysts (e.g., gliomos, menigiomas, acoustic neuromas,lipomas, and/or large tumors); arteriovenous malformation; and/orpituitary gland tumors. In some embodiments, CO₂ laser systems are usedfor the laser incision, excision, ablation, and/or vaporization of softtissue in neurosurgery for the treatment of spinal cord conditions,including: incision/excision and/or vaporization of benign and/ormalignant tumors and/or cysts; intra- and/or extradural lesions; and/orlaminectomy/laminotomy/microdisectomy.

CO₂ laser systems can be used for the incision, excision, and/orvaporization of soft tissue in orthopedic surgery in applications thatinclude arthroscopic and/or general surgery. Arthroscopic applicationsinclude: menisectomy; chondromalacia; chondroplasty; ligament release(e.g., lateral ligament release); excision of plica; and/or partialsynovectomy. General surgery applications include: debridement oftraumatic wounds; debridement of decubitis and/or diabetic ulcers;microsurgery; artificial joint revision; and/or polymer (e.g.,polymethylmethacrylate) removal.

CO₂ laser systems can also be used for incision, excision, and/orvaporization of soft tissue in general and/or thoracic surgery,including endoscopic and/or open procedures. Such applications include:debridement of decubitus ulcers, stasis, diabetic and other ulcers;mastectomy; debridement of burns; rectal and/or anal hemorrhoidectomy;breast biopsy; reduction mammoplasty; cytoreduction for metastaticdisease; laparotomy and/or laparoscopic applications; mediastinal and/orthoracic lesions and/or abnormalities; skin tag vaporization; atheroma;cysts (including sebaceous cysts, pilar cysts, and/or mucous cysts ofthe lips); pilonidal cyst removal and/or repair; abscesses; and/or othersoft tissue applications.

In certain embodiments, CO₂ laser systems can be used for the incision,excision, and/or vaporization of soft tissue in dentistry and/or oralsurgery, including for: gingivectomy; gingivoplasty; incisional and/orexcisional biopsy; treatment of ulcerous lesions (including aphthousulcers); incision of infection when used with antibiotic therapy;frenectomy; excision and/or ablation of benign and/or malignant lesions;homeostasis; operculectomy; crown lengthening; removal of soft tissue,cysts, and/or tumors; oral cavity tumors and/or hemangiomas; abscesses;extraction site hemostasis; salivary gland pathologies; preprostheticgum preparation; leukoplakia; partial glossectomy; and/or periodontalgum resection.

In some embodiments, CO₂ laser systems can be used for incision,excision, and/or vaporization of soft tissue in genitourinaryprocedures, including for: benign and/or malignant lesions of externalgenitalia; condyloma; phimosis; and/or erythroplasia.

EXAMPLE

Surgery was performed to remove portions of the larynx from a dog usinga CO₂ laser system operating at 10.6 microns. The photonic crystal fiberused in this procedure had a hollow core approximately 550 microns indiameter. The fiber had spiral confinement region that included a radialprofile of approximately 20 PES/As₂Se₃ bilayers. The bilayer thicknesswas approximately 3 microns, with a thickness ration of approximately 2to 1 (PES to As₂Se₃). The fiber's cladding was formed from PES, and thefiber's OD was approximately 1500 microns. The fiber was 1.5 m long.

A complete en bloc supraglottic laryngectomy was performed including acordectomy. The laser radiation was delivered using the photonic crystalfiber with a semi-rigid hand-piece. The hand-piece was inserted througha rigid laryngoscope. The input power into the fiber was approximately20 Watts. The radiation power exiting the fiber was approximately 7Watts. Nitrogen was blown through the fiber in the same direction as theradiation. The nitrogen flow rate was approximately 1 liter/min.

Radiation was delivered to the target tissue with a few millimeters(e.g., about 5 mm−1 cm) standoff between the distal end of the fiber andthe target tissue. The supraglottis was removed with just one pause tocauterize any incised blood vessels or to suction any blood away fromthe target area. Minimal bleeding was observed, with blood from incisedvessels coagulating as it was exposed to the output from the fiber. Theprocedure lasted about 45 minutes, during which time the supraglottisand left cord were removed from the dog.

ADDITIONAL EMBODIMENTS

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. An apparatus, comprising: a radiation source configured to provideradiation including radiation having a wavelength λ; an assemblycomprising a radiation input port configured to receive radiation fromthe radiation source and an output port configured to couple theradiation to a photonic crystal fiber, the assembly further comprising aretardation element positioned to modify a polarization state of theradiation received from the radiation source before it is coupled to thephotonic crystal fiber, wherein the reflective retardation elementcomprises a mirror and a retardation layer having an optical thicknessof about λ/4 along a direction about 45° relative to a normal to thesurface of the mirror.
 2. The apparatus of claim 1, wherein the assemblyfurther comprises a gas input port configured to receive gas from a gassource.
 3. The apparatus of claim 2, wherein the photonic crystal fiberhas a hollow core.
 4. The apparatus of claim 3, wherein the output portis further configured to couple the gas received from the gas sourceinto the hollow core of the photonic crystal fiber.
 5. The apparatus ofclaim 2, further comprising the gas source.
 6. The apparatus of claim 1,wherein the retardation element is a reflective retardation element. 7.The apparatus of claim 1, wherein λ is about 2 microns or more.
 8. Theapparatus of claim 1, wherein λ is about 10.1 microns.
 9. The apparatusof claim 1, wherein the retardation element is a transmissiveretardation element.
 10. The apparatus of claim 1, wherein theretardation element modifies the polarization state of the radiationfrom a substantially linear polarization state to a substantiallynon-linear polarization state.
 11. The apparatus of claim 10, whereinthe substantially non-linear polarization state is a substantiallycircular polarization state.
 12. The apparatus of claim 1, wherein theassembly further comprises a focusing element configured to focus theradiation entering the assembly at the radiation input port to a waistnear the output port.
 13. The apparatus of claim 12, wherein thefocusing element focuses the radiation to a waist diameter of about1,000 microns or less.
 14. The apparatus of claim 12, wherein thefocusing element focuses the radiation to a waist diameter of about 500microns or less.
 15. The apparatus of claim 12, wherein the focusingelement is a lens.
 16. The apparatus of claim 15, wherein the lenscomprises Zinc Selenide.
 17. The apparatus of claim 1, furthercomprising the photonic crystal fiber.